I just put my SD MMC card into the card reader and it asked me if i wanted to format it, so i did cos otherwise it wouldnt read it...and now the capacity is FAT 512Kb instead of 128Mb!!! whats going on?
You should never format or delete pix on a memory card whilst it is connected to your system - only do this on the camera itself.
You should also never connect/disconnect whilst the camera is still transferring data; usually there is a flashing small light to indicate that it is still operational.
A thought is that the mechanical write/protect switch on the card to prevent accidental erasures may be enabled; it's similar to the one you find on a floppy and usually there is a "Lock" arrow to indicate the required direction.