be2012 - no appendable media could be mounted - tape is infinite append

I have a B2D job run with a D2T job afterwards. The D2T job is set to Append and terminate if no appendable. I checked the tape and the appendable period is set to Infinte - allow append. The database it is backing up on disk is 300gig. The tape is saying it has 545 gigs left so an append would be possible both with the amount of space left and the tape setting on infinite append.