The Web server (running the Web Site) encountered an unexpected condition that prevented it from fulfilling the request by the client (e.g. your Web browser) for access to the requested URL.
This is a 'catch-all' error generated by the Web server. Basically something has gone wrong, but the server can not be more specific about the error condition in its response to the client. In addition to the 500 error notified back to the client, the Web server should generate some kind of internal error log which gives more details of what went wrong. It is up to the operators of the Web server site to locate and analyse these logs.
If you still see this error in a few hours, please email email@example.com and let me know.