Thank you for your suggestions. I am using TT online, so most of them do not seem to apply. The Federal Review link in the left column online does not give any hint as to what forms might be in play. Clicking into it resulted in the error.
At any rate, the error was gone today. The two things it wanted me to review were both on Schedule E, and one of them seemed to be related to my use of an unsupported character in one of the fields.
