Unlike dedicated eReaders, most tablets are not recognized by ADE.
You need to install and Adobe DRM compatible app such as Blufire on the tablet,
and copy files using a file manager.
Another possibility is a bug in ADE2.0, which is strippy with some devices.
There are lots of bugs in ADE2.0. Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172