For Mac users that are still baffled by this problem here is the fix I used:
1. Go to the document on the Blackberry site which is link
2. Toward the bottom it has a fix but says this does not work for a Mac. What it actually means is that you cannot instal the fix onto your BB from OS X. So, what I did, was to borrow a friends PC and download BB Desktop Managers and the calfix.exe fix on that. I opened Desktop Manager on the PC and then ran the calfix.exe which applied the fix to my BB.
3. I then connected the BB to my Mac via a USB it was immediately recognised as a Mass Storage Device (settings set to turned on) and the media card was accessible in BB Desktop Manager for Mac and in Finder. Further tests revealed it also worked with Missing Sync.
So the answer appears to be borrow a PC to load the patch onto your BB. Annoying that RIM can't be bothered to have provided OS X equivalent to calfix.exe. Anyway, a very frustrating problem easily solved by using your mates PC.
(BB Bold 9700 v220.127.116.112)