i had the same problem shortly after I got my tablet. i thought it was going to be a return to the store job but i managed to fix it. The problem is that it is a generally crap design. The plastic "hinge" bunches up on itself and prevents the catches from locking properly. I fixed mine by using a papderclip to hold the hinge flat while i closed it. Not the best solution but it worked. That said, i have not opened the cover since!
