Hi, I've been developing an app with MacBook Pro (MBP) so far. Last week one of my friends gave me new macbook air 11"(MBA). so Now I can test my code with more than one machine with the same version of developing tools - Both machine has Xcode (3.2.5) and iOS SDK 4.2.1). After some point my app starts get terminated suddenly(iPhone sumulator), and I was using MBP. I got no error message whatsoever. it just stops. I reckon the crash comes from dealing with memory, like 'release'/ 'double-release'. (I'm not 100% sure though). Anyway I thought there must be some mistake within my code for sure. -Confusion starts from this part.- With my MBA, on the other hand, I don'y see any crash. It just works fine. There is nothing different between MBA & MBP except the h/w specifications. Same code, same versions of XCode and iOS SDK. Is the fact that no crash at MBA suggesting that I have to look somewhere else than the code itself? I red some article and Q&As on iOS4.2.1 and XCode 3.2.5 that the most recent version of XCode doesn't recognize the iOS 4.2.1 since the 4.2.1 came out later the 3.2.5. Is it the reason? I have no idea at this moment what should be the next move. thanks