Stupid Questions....
Have you tried to re-import a few of the bad songs?
Is the brand of CD+G you are importing all the same(?), some kind of copy write protection?
You said the last 300 CDG's you imported? Sorry to be blunt
....why wait untill 300 cdg's later to check your work? Why not do a random check after 10 or 25 CD's. Computers are not perfect....it's nice to check once in a while.