A lot of people have reported, and I've personally experienced, where is says this after the first Submit. But it generally works after that. Not sure I've seen reports of multiple Submits failing. Maybe a space is at the beginning or end? Unlikely, but just a thought.
Cheers.
Yeah, basically ignore the error and hit the submit/continue button again. The error will not cause problems. But I wonder how many people fail to get their miles because they give up at this step. Or manually reach out to AA and cause additional customer service calls.