iPhone App runs on iPad-Simulator 3.2 but not on any other Simulator

I'm developing an iPad app with the latest SDK.

if I run it with iPad Simulator 3.2, it works fine. but if I try to run it with any of the other simulators (iPhone Simulator 4.0, iPhone Simulator 4.1, iPhone Simulator 4.2, iPad Simulator 4.2)

the app crashes immediately with this callstack:

#0  0x9113fef6 in __kill
#1  0x9113fee8 in kill$UNIX2003
#2  0x911d262d in raise
#3  0x911e86e4 in abort
#4  0x935edfda in __gnu_cxx::__verbose_terminate_handler
#5  0x014784e7 in _objc_terminate
#6  0x935ec17a in __cxxabiv1::__ter开发者_运维知识库minate
#7  0x935ec1ba in std::terminate
#8  0x935ec2b8 in __cxa_throw
#9  0x01478635 in objc_exception_throw
#10 0x012dc628 in +[NSException raise:format:arguments:]
#11 0x012dc59a in +[NSException raise:format:]
#12 0x0088a6c4 in -[UINib instantiateWithOwner:options:]
#13 0x0088c081 in -[NSBundle(UINSBundleAdditions) loadNibNamed:owner:options:]
#14 0x00696943 in -[UIApplication _loadMainNibFile]
#15 0x006974ca in -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:]
#16 0x006a1db2 in -[UIApplication handleEvent:withNewEvent:]
#17 0x0069a202 in -[UIApplication sendEvent:]
#18 0x0069f732 in _UIApplicationHandleEvent
#19 0x011f3a36 in PurpleEventCallback
#20 0x01305064 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__
#21 0x012656f7 in __CFRunLoopDoSource1
#22 0x01262983 in __CFRunLoopRun
#23 0x01262240 in CFRunLoopRunSpecific
#24 0x01262161 in CFRunLoopRunInMode
#25 0x00696fa8 in -[UIApplication _run]
#26 0x006a342e in UIApplicationMain
#27 0x0000f85a in main at main.m:69

any idea what could cause this?

Thanks!

The stack trace indicates that the app raises an excepting while trying to load the main nib file. Check the full exception message for clues as to what in that nib is causing the problem. Double check the nib for any possible problems.