This happened to me a few weeks ago to. Checked in for a domestic flight and try as I might, I could only print my boarding pass and not my companion's. Very frustrating. Of course I was able to get both tickets from a kiosk at the airport no problem. They gave my companion free TSA pre+, I wonder if maybe that had something to do with it? Can't think of anything else - I've never had a problem before. I hope they fix this glitch.