The server encountered an internal error or misconfiguration and was unable to complete your request.
For fixing this error can only be resolved by fixes to the Web server software. It is not a client-side problem. It is up to the operators of the Web server site to locate and analyse the logs which should give further information about the error.
they can trace the exact reason for the error. Correcting the error may require recoding program logic for the Web server software, which could take some time.
Please see following article: