Will anything move over to the card? Try an individual file and see if it will. If not, then there may be a problem with the card, or there may not be enough room.
Another way to try and move photos, music, videos, etc. over to a SD card would be to plug the tablet into a computer, via USB, and do the moving through the computer, rather than through the tablet. It will give you the option to move more at a time, and also to check the SD card to make sure there is nothing wrong with it, or that it is to full.