I have the same exact issue as described in this thread:
Hi, I have a SMF forum at my site (incom.elementfx.com/smf)
after all those server move issues, my forum is back online but there is a problem when I try to post a message and it gives me this error:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, firstname.lastname@example.org and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
Apache/2.2.10 (Unix) mod_ssl/2.2.10 OpenSSL/0.9.8b mod_mono/1.9 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/18.104.22.16835 Server at incom.elementfx.com Port 80