I have a very long URL on a site hosted on Windows 2003 x64 that looks like this:

http://myhost/a_very_very_long_url_around_300_chars_long

(i.e. a single, very long segment around 300 chars long)

Problem is, I'm getting a 400 Bad Request response from HTTP.SYS (it doesn't even reach IIS). I can tell because these requests show up in system32\LogFiles\HTTPERR, e.g:

2009-09-17 19:51:29 200.123.179.9 3636 192.168.129.50 80 HTTP/1.1 GET /a_very_very_long_url_around_300_chars_long 400 - URL -

I tried setting UrlSegmentMaxLength in the registry and this fixes the issue on my Windows 2003 x86 box but not on the x64 production server. I tried this on another Win2k3 x64 server and it also failed.

Any hints?