I ran into the same thing this year - first time even though I've been a student for years. Though I don't remember if I've ever claimed the training credit before so maybe that's why I'm having trouble just this year.
I ended up just deleting the training credit and then it went through no problem. I would have liked to find a real solution rather than giving that up (or mailing my tax forms), but it's my own fault for waiting until 3 days before the deadline