Internal Server Error message in Manager interface

Does anyone have any idea why I would get this message when I try to change system configuration information. I click save and get this message:

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

Please contact the server administrator, [email protected] 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.

Have you checked the error log in CPanel?

[Wed Apr 19 13:55:55 2006] [error] [client 24.140.83.160] File does not exist: /home/thechris/public_html/500.shtml

Generating this everytime I try to save. But, I have no idea what issparking the dump to 500.

I get the same error when I try to save a new user... is it a php action script somewhere, a JS script?

this is the requested url /manager/index.php?a=30

It has something to do with this :
[Wed Apr 19 14:33:21 2006] [error] [client 24.140.83.160] File does not exist: /home/thechris/public_html/media/script/session.js

and the session information in the config.inc.php. Is there anyway to reset.resynch the session information?