Edit entry error

When I try to save an edit to a guestbook entry 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@marcellusny.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.

This has never happened before. What would cause this? I am using 2.4.2.

Try to edit a different entry. See if it also returns that error.

Yes, if I try to edit any entry I get this error. Any thoughts?

I have reinstalled 2.4.3 and still cannot edit entries. I get the following message when I try to save an edit:

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

I can sign the guestbook and can delete entries, but cannot edit them. Please help.