I have BB curve 8300 with media card. My BB handset recognises Media card when open in explorer, but if I want to use it as Mass storage or through Media manager it did not recognised.
I have ssttings : Mass storage Mode Support on
Auto enabled Mass storage Mode
when connected Yes
I had the same problem and thought it was a bad card. I bought a new card and still the same problem.
With your BB connected,
right click My computer
Manage
Under Storage click on Disk Management.
Change the drive of your card to something off the wall.
The drive letter your card is trying to use is used by something else and therefore can't be recognized by the computer.