The W2 is showing NJ Wages for the PA Resident?  NJ and PA have a reciprocity agreement.  If your client made their employer aware of his residency, the employer would have withheld PA Tax instead of NJ.  Under the circumstances you describe, it sounds like your client will need to file a New Jersey NR with no income to obtain the portion of NJ withholdings.  You would then also provide PA with a copy of the NJNR you filed.  Not sure your client is eligible for a credit on PA due to the reciprocity agreement.