The evening before my trip I printed my boarding passes at home when I did OLCI. The next day I arrived at the BWI airport and used my AA card in the kiosk to obtain dup boarding passes. The kiosk presented my itinerary. It was correct and I pressed "continue".
"You may not check in for this itinerary. You are trying to check in too early. You may only check in 24 hours before departure."
I was one hour from departure. I thought perhaps that I was confused and had travelled to the airport on the wrong day.
However, I already had my home printed boarding docs. I simply proceeded through TSA security and travelled.