As soon as my .htaccess goes over approx 8410 bytes, I get a 500 Internal Server Error.

I don't think this is due to a bad redirect, as I have experimented with redirects in the .htaccess and then with just text that is commented out #. (no actual commands in the .htaccess file)

Is there anything obvious that can cause this?

Update:

The site is on WordPress.

Here are the redirects I was originally trying to add:

RewriteEngine On

## 301 Redirects of old URLs to new
# 301 Redirect 1
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^accesseries/underlay/prod_37\.html$ /product-category/accessories/underlays? [R=301,NE,NC,L]

# 301 Redirect 2
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^accessories/acoustic-underlay/prod_29\.html$ /product/acoustic-underlay/? [R=301,NE,NC,L]

# 301 Redirect 3
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^accessories/cat_4\.html$ /product-category/accessories/? [R=301,NE,NC,L]

# 301 Redirect 4
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-bamboo-flooring/accessories/cat_8\.html$ /product-category/accessories/? [R=301,NE,NC,L]

# 301 Redirect 5
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-bamboo-flooring/bamboo-floor/natural-strandwoven-bamboo-semi-gloss-wide-board-135mm-click/prod_151\.html$ /product/natural-strand-woven-bamboo-semi-gloss-wide-board-135mm-click/? [R=301,NE,NC,L]

# 301 Redirect 6
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-bamboo-flooring/bamboo-floor/strandwoven-chocolate-135mm-bamboo-flooring/prod_174\.html$ /product/strand-woven-chocolate-135mm-bamboo-flooring/? [R=301,NE,NC,L]

# 301 Redirect 7
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-bamboo-flooring/bamboo-floor/strand-woven-kempas-bamboo-flooring/prod_173\.html$ /product/strand-woven-kempas-bamboo-flooring/? [R=301,NE,NC,L]

# 301 Redirect 8
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-bamboo-flooring/bamboo-floor/strandwoven-walnut-wired-135mm-bamboo-flooring/prod_176\.html$ /product/strand-woven-walnut-wired-135mm-bamboo-flooring/? [R=301,NE,NC,L]

# 301 Redirect 9
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-bamboo-flooring/cat_7\.html$ /product-category/bamboo-floor/? [R=301,NE,NC,L]

# 301 Redirect 10
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-bamboo-installation/info_8\.html$ /bamboo-installation/? [R=301,NE,NC,L]

# 301 Redirect 11
RewriteCond %{QUERY_STRING}  ^act=cart$ [NC]
RewriteRule ^cart\.php$ /cart/? [R=301,NE,NC,L]

# 301 Redirect 12
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^contact-us/info_2\.html$ /contact-us/? [R=301,NE,NC,L]

# 301 Redirect 13
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^faqs/info_9\.html$ /faqs/? [R=301,NE,NC,L]

# 301 Redirect 14
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-floating-timber-floor/black-butt-engineered-floating-timber/prod_213\.html$ /product/black-butt-engineered-floating-timber/? [R=301,NE,NC,L]

# 301 Redirect 15
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-floating-timber-floor/doussie-engineered-floating-timber/prod_208\.html$ /product/doussie-engineered-floating-timber/? [R=301,NE,NC,L]

# 301 Redirect 16
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-floating-timber-floor/smoked-oak-engineered-floating-timber/prod_217\.html$ /product/smoked-oak-engineered-floating-timber/? [R=301,NE,NC,L]

# 301 Redirect 17
RewriteCond %{QUERY_STRING}  ^act=thanks$ [NC]
RewriteRule ^index\.php$ http://www.xxxxxxxxxx.com/? [R=301,NE,NC,L]

# 301 Redirect 18
RewriteCond %{QUERY_STRING}  ^act=viewCat&catId=13$ [NC]
RewriteRule ^index\.php$ /product-category/samples/bamboo-flooring-samples/? [R=301,NE,NC,L]

# 301 Redirect 19
RewriteCond %{QUERY_STRING}  ^act=viewCat&catId=18$ [NC]
RewriteRule ^index\.php$ /product/bamboo-plastic-composite/? [R=301,NE,NC,L]

# 301 Redirect 20
RewriteCond %{QUERY_STRING}  ^act=viewCat&catId=2$ [NC]
RewriteRule ^index\.php$ /product-category/bamboo-floor/? [R=301,NE,NC,L]

# 301 Redirect 21
RewriteCond %{QUERY_STRING}  ^act=viewCat&catId=20$ [NC]
RewriteRule ^index\.php$ /products/? [R=301,NE,NC,L]

# 301 Redirect 22
RewriteCond %{QUERY_STRING}  ^act=viewCat&catId=3$ [NC]
RewriteRule ^index\.php$ /product-category/floating-timber-floor/? [R=301,NE,NC,L]

# 301 Redirect 23
RewriteCond %{QUERY_STRING}  ^act=viewCat&catId=5$ [NC]
RewriteRule ^index\.php$ /product-category/laminate-flooring/? [R=301,NE,NC,L]

# 301 Redirect 24
RewriteCond %{QUERY_STRING}  ^act=viewCat&catId=6$ [NC]
RewriteRule ^index\.php$ /product-category/accessories/? [R=301,NE,NC,L]

# 301 Redirect 25
RewriteCond %{QUERY_STRING}  ^act=viewCat&catId=saleItems$ [NC]
RewriteRule ^index\.php$ /product-category/clearance-sale/? [R=301,NE,NC,L]

# 301 Redirect 26
RewriteCond %{QUERY_STRING}  ^act=viewDoc&docId=3$ [NC]
RewriteRule ^index\.php$ /faqs/? [R=301,NE,NC,L]

# 301 Redirect 27
RewriteCond %{QUERY_STRING}  ^act=viewDoc&docId=4$ [NC]
RewriteRule ^index\.php$ /faqs/? [R=301,NE,NC,L]

# 301 Redirect 28
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=137$ [NC]
RewriteRule ^index\.php$ /product/laminate-flooring-goustein-wood/? [R=301,NE,NC,L]

# 301 Redirect 29
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=164$ [NC]
RewriteRule ^index\.php$ /product/modern-black-brushed-finish-strand-woven-flooring/? [R=301,NE,NC,L]

# 301 Redirect 30
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=165$ [NC]
RewriteRule ^index\.php$ /product/lime-wash-strand-woven-bamboo-flooring/? [R=301,NE,NC,L]

# 301 Redirect 31
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=168$ [NC]
RewriteRule ^index\.php$ /product/country-bark/? [R=301,NE,NC,L]

# 301 Redirect 32
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=173$ [NC]
RewriteRule ^index\.php$ /product-category/bamboo-floor/14mm-bamboo-flooring/? [R=301,NE,NC,L]

# 301 Redirect 33
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=178$ [NC]
RewriteRule ^index\.php$ /product/blue-gum-136-floating-timber/? [R=301,NE,NC,L]

# 301 Redirect 34
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=199$ [NC]
RewriteRule ^index\.php$ /product/jarrah-laminate-floor-sample/? [R=301,NE,NC,L]

# 301 Redirect 35
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=205$ [NC]
RewriteRule ^index\.php$ /product/elm-12mm-laminate-floor-sample/? [R=301,NE,NC,L]

# 301 Redirect 36
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=209$ [NC]
RewriteRule ^index\.php$ /product/iroko-engineered-floating-timber/? [R=301,NE,NC,L]

# 301 Redirect 37
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=222$ [NC]
RewriteRule ^index\.php$ /product/european-oak-engineered-floating-timber-sample/? [R=301,NE,NC,L]

# 301 Redirect 38
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=236$ [NC]
RewriteRule ^index\.php$ /product/black-forest-5mm-vinyl-flooring/? [R=301,NE,NC,L]

# 301 Redirect 39
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=65$ [NC]
RewriteRule ^index\.php$ /product/stair-nose/? [R=301,NE,NC,L]

# 301 Redirect 40
RewriteCond %{QUERY_STRING}  ^act=viewProd&productId=83$ [NC]
RewriteRule ^index\.php$ /product/laminate-flooring-warm-teak/? [R=301,NE,NC,L]

# 301 Redirect 41
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-laminate-flooring/12mm-laminate-flooring/blackbutt/prod_156\.html$ /product/blackbutt-12mm-laminate-floor/? [R=301,NE,NC,L]

# 301 Redirect 42
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-laminate-flooring/12mm-laminate-flooring/tasmanian-oak/prod_171\.html$ /product/tasmanian-oak/? [R=301,NE,NC,L]

# 301 Redirect 43
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-laminate-flooring/8-3mm-laminate-flooring/laminate-flooring-warm-teak/prod_8\.html$ /product/laminate-flooring-warm-teak/? [R=301,NE,NC,L]

# 301 Redirect 44
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-laminate-flooring/accessories/cat_6\.html$ /product-category/accessories/? [R=301,NE,NC,L]

# 301 Redirect 45
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-laminate-flooring/cat_5\.html$ /product-category/laminate-flooring/? [R=301,NE,NC,L]

# 301 Redirect 46
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-laminate-flooring/country-classic-12mm-laminate/cat_19\.html$ /product-category/laminate-flooring/12mm-country-classic-laminate-floor/? [R=301,NE,NC,L]

# 301 Redirect 47
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-laminate-installation/info_7\.html$ /laminate-installation/? [R=301,NE,NC,L]

# 301 Redirect 48
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^privacy-policy/info_4\.html$ /faqs/? [R=301,NE,NC,L]

# 301 Redirect 49
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^-quotation-request/info_5\.html$ /quotation-request/? [R=301,NE,NC,L]

# 301 Redirect 50
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^rainbow-flooring/cat_16\.html$ /product-category/rainbow-flooring/? [R=301,NE,NC,L]

# 301 Redirect 51
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^rainbow-flooring/walnut-rainbow-flooring/prod_112\.html$ /product/walnut-rainbow-flooring/? [R=301,NE,NC,L]

# 301 Redirect 52
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/12mm-laminate-floor-samples/kempas-laminate-floor-sample/prod_195\.html$ /product/kempas-laminate-floor-sample/? [R=301,NE,NC,L]

# 301 Redirect 53
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/12mm-laminate-floor-samples/spotted-gum-laminate-floor-sample/prod_196\.html$ /product/spotted-gum-laminate-floor-sample/? [R=301,NE,NC,L]

# 301 Redirect 54
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/12mm-laminate-floor-samples/tasmanian-oak-laminate-floor-sample/prod_197\.html$ /product/tasmanian-oak-laminate-floor-sample/? [R=301,NE,NC,L]

# 301 Redirect 55
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/bamboo-flooring-samples/cat_13\.html$ /product-category/samples/bamboo-flooring-samples/? [R=301,NE,NC,L]

# 301 Redirect 56
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/bamboo-flooring-samples/rosewood-strandwoven-bamboo-floor-135mm-click-sample/prod_191\.html$ /product/rosewood-strand-woven-bamboo-floor-135mm-click-sample/? [R=301,NE,NC,L]

# 301 Redirect 57
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/cat_9\.html$ /samples/? [R=301,NE,NC,L]

# 301 Redirect 58
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/floating-timber-floor-samples/iroko-engineered-floating-timber-floor-sample/prod_223\.html$ /product/iroko-engineered-floating-timber-floor-sample/? [R=301,NE,NC,L]

# 301 Redirect 59
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/floating-timber-floor-samples/jarrah-engineered-floating-timber-sample/prod_224\.html$ /product/jarrah-engineered-floating-timber-sample/? [R=301,NE,NC,L]

# 301 Redirect 60
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/floating-timber-floor-samples/merbau-engineered-floating-timber-sample/prod_226\.html$ /product/merbau-engineered-floating-timber-sample/? [R=301,NE,NC,L]

# 301 Redirect 61
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/floating-timber-floor-samples/spotted-gum-engineered-floating-timber-sample/prod_228\.html$ /product/spotted-gum-engineered-floating-timber-sample/? [R=301,NE,NC,L]

# 301 Redirect 62
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^samples/floating-timber-floor-samples/sydney-blue-gum-engineered-floating-timber-sample/prod_220\.html$ /product/sydney-blue-gum-engineered-floating-timber-sample/? [R=301,NE,NC,L]

# 301 Redirect 63
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^shop\.php/-laminate-flooring/accessories/laminate-flooring-accessories-click-stairnose/prod_251\.html$ /product/stair-nose/? [R=301,NE,NC,L]

# 301 Redirect 64
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^shop\.php/-laminate-flooring/country-classic-12mm-laminate/country-classic-polar-white/prod_243\.html$ /product/country-classic-polar-white/? [R=301,NE,NC,L]

# 301 Redirect 65
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^shop\.php/samples/12mm-laminate-floor-samples/country-classic-polar-white/prod_244\.html$ /product/country-classic-polar-white-sample/? [R=301,NE,NC,L]

# 301 Redirect 66
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^shop\.php/samples/12mm-laminate-floor-samples/rustic-oak-12mm-laminate-floor/prod_248\.html$ /product/rustic-oak-12mm-laminate-floor-sample/? [R=301,NE,NC,L]

# 301 Redirect 67
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^shop\.php/samples/vinyl-flooring-samples/cat_25\.html$ /product-category/samples/vinyl-flooring-samples/? [R=301,NE,NC,L]

# 301 Redirect 68
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^shop\.php/vinyl-flooring/cat_24\.html$ /product-category/vinyl-floor/? [R=301,NE,NC,L]

# 301 Redirect 69
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^solardeck-tiles/cat_22\.html$ /product-category/solardeck-tiles/? [R=301,NE,NC,L]

# 301 Redirect 70
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^solardeck-tiles/solardeck-tiles/prod_206\.html$ /product/solardeck-tiles/? [R=301,NE,NC,L]

# 301 Redirect 71
RewriteCond %{QUERY_STRING}  ^$
RewriteRule ^terms-conditions/info_3\.html$ /faqs/? [R=301,NE,NC,L]

I'm getting errors like this in my log:

Invalid command 'aminate-flooring/tasmanian-oak/prod_171\\.html$', perhaps misspelled or defined by a module not included in the server configuration, referer: http://www.xxxxxxxx.com/laminate-installation/

Invalid command ',NE,NC,L]', perhaps misspelled or defined by a module not included in the server configuration

Invalid command ',L]#', perhaps misspelled or defined by a module not included in the server configuration