The question is definitely unlikely to help future visitors. The title only conveys that some unspecified error occurred while working with RSA Decryption, and the problem is almost entirely obscured by red herring code blocks. What was the error? The OP forgot to decode the the encrypted string before passing it to
doFinal. That was it.
I sincerely doubt this will help anyone in the future, since 90% of the time this sort of problem is already identified (or at least should be) on your first readthrough after you hit an exception. You shouldn't post to SO first, then do the your due diligence in terms of debugging and post that as an answer.