I am using Uploadify to provide progress bar support for file uploads on a PHP app I built. It works perfectly for a few uploads,then every few uploads it fails and the data from the $_FILES array reveals an UPLOAD_ERR_CANT_WRITE error. (Error code 7). I ran Paros proxy between my browser and the server to see the difference between a passing and failing request. The only difference was the content separator for the multi-part post which changes every time. I would conclude this was fully a server error, except with a plain jane form, I cannot reproduce the error. I am not a server guy, so please let me know what information is needed to troubleshoot this and I will update the question with those details. I did place these lines in the .htaccess, but to know avail. The site is hosted on Rackspace Cloudsites so my configuration options are limited: <IfModule mod_security.c> SecFilterEngine Off SecFilterScanPOST Off </IfModule> php_value upload_max_filesize 10M php_value post_max_size 10M php_value max_execution_time 200 php_value max_input_time 200