[problem] 1 user has a lot of Session Timeout Errors

[ups]

One of ours users is having a tremendous number of timeout errors when posting.
Sometimes, he needs to re-submit the post 10 or 30 times until the forum accepts it: most of the times he simple gives up.

Troubleshooting is getting difficult:
Using SMF 2.0 RC5
No error messages appear.
Me and other admins don't have any problems.
Cleared sfm_sessions table and renamed the cookie. Problem still happens.

He is using Firefox on windows (default firewall) but I think it happens with other browsers as well.

What can I do to troubleshoot this?

[IchBin™]

I suppose a firewall or anti-virus program could be causing such a problem. Does he have the same problem from another computer? There's not much you can do when he's the only one having the problem as it's obviously something on his end.