You'd really like command line access to the server to debug 500s (or access to it's logs). If you can run the script from the command line, you usually get a more informative error message. The same message would end up in the logs.
If you have neither access, try using Carp qw/fatalsToBrowser/ and replacing your use with a require - possibly in an eval block. That should route the error message to the browser rather than to the server logs by moving the loading of the module to run-time rather than compile time.
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"As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs."
--Maurice Wilkes