Application failed to start

I have this encryption class that lives in the lib folder. I use it to
encrypt and decrypt credit card numbers. On my local copy of the app on
my machine it runs fine, but on the app that lives on the server I get
"Application failed to start properly" whenever I hit the submit button
to add a credit card. I imagine this is a configuration issue, but I
don't know how to fix it. Does anyone have any ideas? Thanks,

-S

What error is showing up in your production.log