No mate it's not a problem with the phone itself,
you might have changed something about the settings, so highly recommending check them again,
if not , you might just need to update your software,
been there once !
Hey,
check this out:
Uploading from the Web App (Computer)
sign in to Google Play on your computer and upload it through there. Just go to Books -> My Books and then select Upload Files.
Uploading from the Web App (Nexus 7)
You can also do the above directly from the Chrome browser on your...