I have a Nextbook2 & I'm having a problem. It has been working fine but now I can't read the books I've downloaded to it. It says 'The book has been damaged, can not be opened.' I downloaded one book & read a couple pages just fine. The next day I turned on the Nextbook, opened the book & got that annoying message. Does anyone have any idea why my ereader won't let me read? It does have an Android OS. Thanks!