Not able to post using web editor

Hi there,
I am using WP 2.8.4 for my blog. I am facing an issue since the upgrade that I am not able to post any long posts over my blog. Post of few lines work, few lines means, 5-8 lines. For anything beyond that, I am getting the following error while attempting to post or trying to save it as draft.

Whenever I try to post a long post, I get the following error,
Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, webmaster@myblogsite.com 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/2.0.63 (Unix) mod_ssl/2.0.63 OpenSSL/0.9.8e-fips-rhel5 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 Server at <my blog site> Port 80

Any help to resolve this would be highly appreciated. Please note that before the upgrade, everything was working fine.

With thanks and regards