There really isn't enough information to go on. Note that the API allows one to add, update, and save metadata items after a media object is created, but this hasn't really been tested much because the UI effectively gives you a read-only view of metadata.
The best I can suggest is to fire up the debugger and start digging in. Let us know if you find a bug that must be fixed. I plan to add editable metadata in the 2.5 timeframe (maybe a year or so away).
Roger Martin
Creator and Lead Developer of Gallery Server Pro