Sorry for the delay in responding. The Backflip is quickly getting a reputation for it's limitations and locked down features...
http://androidandme.com/2010/03/news/att-the-most-crippled-android-experience/With that said, you should be able to enable 3rd party devices via something like...
Settings --> Applications --> check Unknown sources.
Otherwise, it's best to check with their support. This has nothing to do with the functionality of MMP on the droid, rather, AT&T's implementation. Please let me know if you still have issues. Happy to help.
Best,
Tim