A 500 error usually means that there has been a problem running the script or connecting to the database. If you are using Internet Explorer you may have to turn off "Friendly HTTP Error Messages" before you will get any useful information. To do this, go to Tools >> Internet Options... >> click the Advanced Tab >> Uncheck the "Show Friendly HTTP Error Messages" option. Once you have turned off the Friendly HTTP Error messages, you should get an error that is a little more descriptive which may help you troubleshoot your problem.