jod im no expert but i have a dell dimention 4800 with a dvdr/cdr/w burner and i noticed that my pc wont read some kinds of the dvd-r discs so ot might be the media your using +R insted of -R and see if that works....
after you have converted your .AVI file with DVD Santa you can burn it useing Clone DVD2 if you use the Image burning section (The Third One )in clone dvd2 you just have to put into clone DVD 2 the file path where DVD Santa has put the converted file.
Was the conversion successful? If yes, then you can always burn with some other programs (e.g. Nero). DVDSanta is not that good at burning anyway.