i think u should have bought the 8 G memory stick pro duo because it works just fine
You need to update your PSP, this will require a card your PSP recognises, you should have been supplied with a card when you bought your PSP, the 4GB and 8GB cards are only supported by newer updates. Download the update from the playstation website and then try using your 1GB Card, Also try formatting your memory card again...
and one other thing it may be a fake memory...see this video ...SONY MEMORY STICK PRO DUO WARNING 16GB 32GB - YouTube and this one too
Fake 4GB Sony Memory Stick Pro Duo from Ebay - YouTube
if u r sure its not fake
i will search for more info. and reply u again