Warning: Unable to find symbols for....

Hi, we have an app that has been working fine under 2.2.1, both in simulator and on phone. I just upgraded my phone os to 3.0 and now the app does not run. It clears the screen like it's going to start, but it then quits back to the main iPhone screen. However, if I run the Debug 3.0 build on the device, it runs fine. Is there something I'm missing?
Thanks!
Phil