Memory overload?

Hello!

Im building a toy with arduino and an Rfid-reader. Everything is working just fine with the reader, detecting the different Rfid's and giving me the correct feedback. But after a while it seems like some kind of internal storing memory gets overloaded, and it stops functioning. This happens faster if I feed the reader with different Rfid-chips. If I feed it the same chip I can go on forever.. Must I reset some storing fascilities? I have read about Sram, it might be this component that gets overloaded? The code itself is not more than 5500 byte, so I dont think this is the problem. The exact same thing happens on the Arduino NG Im using for prototyping and testing and on the Arduino Mini that Im using in my model. Does nybody know what I should try? I'm planning to have at least 16 different id's in the code at last and so far I've just included seven..

Thanks in advance if anybody experienced the same..

Sara