For some reason this was being sent to the clients as something like this:
What makes it strange is that we can't duplicate the issue when viewing the site on the server, but we get the issue when viewing the site from Client PC's.
We've tried disabling all firewalls, and antivirus software. We've checked it on IE and Firefox, and we've checked that there is no proxy specified in the browsers. Unfortunately the server is on a client's network so we have very little control over the environment that is being used. Anyone have any suggestions?