Default Problem with my O2 XDA II

I use O2 XDA2 with SD Card 512MB. My problem is that: I plug SD card in my O2 anh my O2 can find the SD Card. Anh is similar if I you Microsoft Active Sync. But sometimes,when I use data contained in my Card, my O2 can't recognize my SD card. I only use 15% of my Card's size but in setting it's alway 100%. Sometimes, when I play games or listen musices which are installed in my SD Card, all data in my SD card suddenly disappear. So I think that, the problem may be the tangential point between my O2 anh my Card is not good.
How can I do to solve this problem? I wish, you can help me. Thanks very much!!!

P/s: May be I can type something wrong, but those all I can to describle my prolem . :roll: