We've hit a similar glitch but for different reasons. Hanni is having particular difficulty with one sort of thing, and while at the beginning there were several kinds of games to choose from, she seems to have completed all lines of advance until she gets past this one bottleneck.
For your problem, I wonder if your kid made errors on pretest games that he should have been able to pass, and/or if he started at the wrong grade level? If either of these is the case, you could try starting over by creating a new account for him with a different name. I did this, because I made some mistakes in how I set up Hanni to begin with.
Another possibility is that he's simply playing too carelessly for Dreambox's algorithm to figure out what he knows, in which case it might not be a good fit for him.
