How long is Social Security allowed to investigate an overpayment issue?

If you are suing SSA in Federal Court then you already must know their position as it will be contained in their answer to your lawsuit. it is unclear to me how you have a overpayment though, if your checks were stolen.

Jonathan, to anwer your question, they have never followed through with getting me proof of their claim that I cashed both checks, so because of that the investigation has never been closed, and I wound up paying for the overpayment anyway, because I did not know about POMS Section GN 02406.310, so I let them take the money out, while awaiting the copies of the 2 forged checks, as well as the FMS-1199 form from the treasury department. So in short, when it comes to Social Security, they assume you cashed the checks until you prove otherwise, and I have not been able to prove otherwise because they have not furnished me with the evidence against me.

If you are suing them, you should make a discovery request for the cancelled checks to their attorney. If this has been going on since 2005, it does not seem likely they will provide the information you have requested on their own initiative.