I'm guessing that your URL change is unrelated to the error.
A 500x error usually means a server side processing error, like unable to render the page or there's bug in the server side code on the page (PHP, ASPX, etc). 400x errors typically mean the page doesn't exist.
Since Google is showing you a 500 error, are you sure it's because the file doesn't exist? You said you changed the URL. Did you rename the file or something that would cause your server to not know how to render the file? Could the old file still exist, but when Google tries to crawl it, the server can't process because of a code change?