Problems Posting / Form Is No Longer Valid Error

Some browsers seem to have issues with the underscore character ("_"). It then gives the following errors when you try to post:

The form you have submitted is no longer valid.

Warning: Unknown: The session id contains illegal characters, valid characters are a-z, A-Z, 0-9 and '-,' in Unknown on line 0

If you have an underscore in your logon name or display name:

* In your PROFILE area, remove the underscore from your name
* Log out of the forums
* Clear all cookies
* Stop and start the browser
* Log back in again

That seems to resolve many issues. I've heard for example that people with underscores can post in FireFox but not in IE. It's best not to have underscores.