400 Bad Request on new server

I have recently moved a couple wordpress installs over to a clients server and have run into a new error.

Bad Request

Your browser sent a request that this server could not understand.
Request header field is missing ‘:’ separator.

CC

Now this only happens in firefox (clearing the cookies worked for a bit but now the error is back), but since it doesnt happen on my development server it tells me it must be something wrong with either my server config, my php config, or my sql config.

Are there any known issues that cause this with MySQL 4.1.22 Apache 2.2.11 or PHP 5.3.0 in a windows enviroment?

(My development server was unix, while my clients server is windows server 2008)