I got the PB when it was released and wasn't able to back up out of the box. About a month into using it and trying unsuccessfully to back up I did a security swipe. I was able to back up once and never again. I tried again right after the OS 2 update, no luck, so I swiped it again. I reconfigured the backup to hack up everything except the media files (3 movies,300 songs and maybe 500 or pictures - not a lot) and it has been working everytime now, knock on wood. Good luck.
I have had the same problem(on a 16gb model)
For me it would never sync media, only video's and pictures. I use to just wifi move my files into their corresponding folder. (it also wouldn't backup, which is why I am writing this)
I too got the one lucky backup. Since I then, I pretty much replicated that backup, and it has worked fine (both backup and sync)
First you, um... Plug it in
Then you start the whole backup thing
Touch the playbook and the pc/mac occasionally so it doesn't go to sleep/standby mode
Also, make sure you can sync files from you computer (sometimes it will recognize pb but doesn't let my sync)
Honestly I really think its a DM issue. Usually what will fail to backup is the application data. The media and settings back up just fine from a selective backup.
The backup wouldn't work on my brand spanking new Samsung laptop running Win7. On my older xp computer downstairs though, it backed up fine no problems. Go figure. If I would have to put the blame somewhere it would have to be DM. You could try re-installing it, but from other people that have tried that, including myself, it did not solve the problem. Really hope it gets fixed soon.
I wish RIM had smarter programmers that were able to make software that works without so many bugs. I do love their products but I have to admit they are about the buggiest things made. One of the reasons they are losing so many. Hope it doesn't continue when bb10 is out.
Have had no problems with complete backup on my PB. I don't how people have so many issues. The Playbook provides far fewer issues to me than I have with our IPAD and the whole frustrating issues with ITUNES.