I don't know if you were able to resolve this, but it appears that others are also having issues with the backup hanging on Smart Card. For some, they are able to complete the backup by waiting about 10 minutes. Others have disabled the Smart Card option for backup and everything else backed up.
Keep pulling the battery, it took me 7hours, but it finally rebooted. If you see a small icon on the screen tap it and it will continue. I must have pulled the battery 10 times to get it to finish the download. It works very slowly so be patient.
I am very happy to report back to you all that I have found a workaround that has worked for me.
Give this a try:
Go in the Back Up, select Custom and select the box next to Data type (so that you can back up everything) or select the fields you need BUT, before hitting that Back Up button, EXCLUDE SOCIAL FEEDS DATA FROM THE BACK UP BY UNCHECKING THE SOCIAL FEEDS BOX!
Please let me know if it works for you & if not, please tell me your model, your OS version & the version of DM that you are running.
DM is really annoying. I have tried to back up my phone and it freezes on Smart Card. And found this thread, so I did the custom back up and unchecked the Smart Card, now DM froze again on Shortcut Settings. It seems like DM freezes on the last part of the back up. What's up with RIM?!
I noticed the same thing yesterday backing up my 9900. It got to Smart Card and stalled. I just left it alone for a few minutes. It eventually completed the backup.