Under a strict reading of the law, you are liable as the endorser of the check (you signed the back) to the check cashing store. You have a claim against the Company for not honoring is check. You may also have a defense if the check cashing store waited too long to notify you of the bad check. This is a very unforunate occurrence, but you probably can get some free advise from the NJ Dept. of Labor as you have not been paid for work performed.