What happens when you download apps? Error? Nothing? Where are you getting the apps from? Play Store?

You should have plenty of room to download and install apps.

 

That total is weird though: a large, negative amount used (just less than -2^35 bytes) out of a total of zero.

I'd almost be tempted to speculate about a false negative caused by twos-complement numbers, but a positive value large enough to cause that seems implausible. A stuck bit somewhere? Something is very confused anyway.

 

Maybe something funky happening with the software. Have you tried rebooting the tablet?

 

its a weird error. try removing the sd card and reset the device. make sure its data is backed up