[lode]

Something similar happened to me monday. Turned out the disc was saying sayonara.
It was writing files that was the trouble for the disc, and after I swapped disc everything seems fine again.

PT recorded just fine, but playback of the recording made PT beachball.
I got no errormessages when reopening the session, but playback still didn´t work.

Not even Finder could read/copy the files that were corrupt.

It´s not exactly the same symptoms, but I would try switching the HDD.