PROBLEM Server error detected on update plugin

[cobber]

Morning,

the site http://get-simple.info is ok. It's when I log in and try to update zip file to extend 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 to inform of the time the error occurred and of anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Thanks