A 500 error is an error in the web-server, to resolve it you have to report it to the person who administers that website.
5xx Server Error
The server failed to fulfill an apparently valid request.
Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has encountered an error or is otherwise incapable of performing the request. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents should display any included entity to the user. These response codes are applicable to any request method.
500 Internal Server Error
A generic error message, given when no more specific message is suitable.
I've seen this associated with PHP and Blogspot, so there may be a PHP/Blogspot bug or server-side coding error that produces this message at the server end under some circumstances.