How many apps do you have on the sdcard? It might be a bit of a pain, but move all of your apps back to internal storage (if you have room), connect you phone to your computer and mount it as usb storage (or use any file browser capable of viewing hidden directories), and delete the .android_secure directory that is in the top level of the sdcard. Once that is done, start moving apps back to the card, and see if you can update them.