[wejones]

Yes, this has been mentioned quite often. Apparently it is the number of transponders that gets maxed out, because the thing comes with memory more than half full of transponders already, and each time you do a blind scan, you add a few more new transponders that are really the same ones, but differ slightly.
If you have the serial line connected to a computer, and have the Gtools channel editor, run that, and upload the memory from the Ultra to the computer, then look at the "Information" panel along the left side near the bottom, and look at where it says TpCnt = ?/1300 . My guess is that the "?" will be greater than the 1300 maximum. When your exact symptoms happened to me, I was up around 1500 or 1600 . I went in and removed all satellites that I don't use, and all transponders that I don't use, and got down to about 500 transponders, and now I don't have the problem. Other people remove transponders manually, but that is a lot of work. It's easy with the Gtools program.