What I do is
1. Take out the MMC from BB
2. Insert it with MMC reader, and plug in to PC
3. Move all the data inside MMC to PC
4. Format the MMC
5. Plug out the MMC, then insert it into BB
6. Switch on the BB with empty (formated) MMC
7. Plug in BB with cable data to PC
8. Move all the data that stored from PC