I have a tab 10.1, running a TWM copy of Jellybean. Ever since I upgraded from Gingerbread to ICS and then to JB, I've had this issue with not being able to download new apps via the store, or even if I email it to myself. I have tried just about everything, from checking if Download manager is enabled, to doing a factory reset...installing a fresh version of OS...removing and then re-adding my gmail account. NOTHING worked. Funny thing is though, when upgrading to JB, I accidently used a WiFi-only version....and yet when I connected to a WiFi spot, I could download apps!! That was the ONLY version that worked. I am literally torn whether I should continue battling with this, or just chuck the thing in the damn trash!