If you are getting an Error 500, then the server has encountered an "internal" error.
The easiest way to identify the cause is to find the server log file, and look at what exception was thrown!
Assuming you are using
TomCat on a local machine then by default the exception will be written to localhost.yyyy-mm-dd.log in your logs sub-directory. Where yyyy-mm-dd is the current date, and the logs sub-directory is usually under the parent tomcat install directory.
For neatness it is sometimes best to stop tomcat, delete ALL the log files, start tomcat then open the URL that is causing the error.
If you need any help diagnosing the error then post the exception details from the log file.
Rufus.