Yeah, I know this problem. I also got into similar situations a while ago. I think PrettyFaces simply rethrows exceptions from action methods and Mojarra swallows the details. Is this correct?
My workaround was to wrap the action method in a big try-catch block and log all the details there. This way you can find out which exception is thrown and why. You can then catch the specific exception type and display a corresponding message to the user.
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