Photo uploading problems!

Hi all, can anyone help?
For about two months I have been unable to upload photos. As a forum moderator the size of my files is not limited yet I cannot upload any photos at all. I get the following message every time I try -
Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@mycockpit.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.

This is becoming very annoying as I am only able to upload my pictures at other sites and here is where they really should be! Matt, any chance you can fix it, my emails don't seem to be getting to you!

I have made great progress on my sim and have some new products to display...

Cheers Gwyn