Unfortunately yes, if you were overpaid in error, you have to return the money. It's as simple as this: the money is not yours, and you have no right to it. Just as if you had accidentally paid a store or serviceperson too much and would have the right to get it back, the retirement fund, etc. has the right to its overpayment back.It would reasonable to work out a payment schedule, since it was an innocent mistake, rather than have to pay it all at once.Also, you might first have an attorney check any pension, disability, employment agreement, etc. documents your husband had, as well as the recent correspondence--possibly you are owed something. Before you give the money back, it's worth checking--you've already seen that the fund, etc. can make mistakes in its accounting.