iphone app blank in simulator: moved from 3.1.3 to 4.1

I have a 3.1 xcode project that has been running my app just fine under the 3.1.3 version of the OS. I've been testing this app on my iphone 3G ( not running IOS 4 ).

I just copied over the XCode project and files, downloaded the latest XCode 3.2.4 with the 4.1 SDK. When I run my application via the simulator it just comes up blank instead of showing my app. I can see via the NSLog statements that it's actually getting to my initWithFrame() and viewDidLoad() methods but it's like it didn't load the images correctly. I've tried copying the files back into the xcode project and allowing it to update references. I've also tried using 4.0 and 4.1 of the SDK along with the iphone 4 and iphone simulators under hardware.

I do see some errors from system.log:

Sep 20 21:59:01 s-macbook-pro-17 [0x0-0x18018].com.apple.Xcode[484]: Xcode(484,0x7fff70216c20) malloc: reference count underflow for 0x2019c0a40, break on auto_refcount_underflow_error to debug.
Sep 20 21:59:01 s-macbook-pro-17 Xcode[484]: Xcode(484,0x7fff70216c20) malloc: reference count underflow for 0x2019c0a40, break on auto_refcount_underflow_error to debug.
Sep 20 21:59:03 s-macbook-pro-17 com.apple.launchd.peruser.502[127] (com.apple.iPhoneSimulator:com.apple.managedconfiguration.profiled): Bug: launchd_core_logic.c:4598 (24108):2
Sep 20 21:59:03 s-macbook-pro-17 com.apple.launchd.peruser.502[127] (com.apple.iPhoneSimulator:com.apple.managedconfiguration.profiled): Path monitoring failed on "/Users/m/Library/Application Support/iPhone Simulator/4.1/Library/ConfigurationProfiles/profiledRunning": No such file or directory
Sep 20 21:59:03 s-macbook-pro-17 com.apple.launchd.peruser.502[127] (com.apple.iPhoneSimulator:com.apple.managedconfiguration.profiled): Bug: launchd_core_logic.c:4598 (24108):2
Sep 20 21:59:03 s-macbook-pro-17 com.apple.launchd.peruser.502[127] (com.apple.iPhoneSimulator:com.apple.managedconfiguration.profiled): Path monitoring failed on "/Users/m/Library/Application Support/iPhone Simulator/4.1/Library/ConfigurationProfiles/MCOutstandingNagComputation": No such file or directory
Sep 20 21:59:03 s-macbook-pro-17 com.apple.launchd.peruser.502[127] (com.apple.iPhoneSimulator:com.apple.managedconfiguration.mdmd): Bug: launchd_core_logic.c:4598 (24108):2
Sep 20 21:59:03 s-macbook-pro-17 com.apple.launchd.peruser.502[127] (com.apple.iPhoneSimulator:com.apple.managedconfiguration.mdmd): Path monitoring failed on "/Users/m/Library/Application Support/iPhone Simulator/4.1/Library/ConfigurationProfiles/MDMOutstandingActivities.plist": No such file or directory
Sep 20 21:59:03 s-macbook-pro-17 vot[929]: ******** AX INSPECTOR MODE ************ 
Sep 20 21:59:03 s-macbook-pro-17 vot[929]: **** Running VoiceOver Lite ****
Sep 20 21:59:06 s-macbook-pro-17 app[935]: MainView alloc
Sep 20 21:59:06 s-macbook-pro-17 app[935]: MainView alloc complete
Sep 20 21:59:06 s-macbook-pro-17 app[935]: loadView 开发者_开发技巧complete

I set the "Visible at launch" property on the main window via interface builder. I didn't have this set in my xcode project on my other macbook pro when using XCode 3.1.

I came across this thread that helped me:

iPhone SDK4.0 and xcode 3.2.3 issue

Similar situation in my app, but my problem was that somehow, in the MainWindow.xib in IB, the File Owner's delegate was no longer linked up to my app delegate (right click on File Owner in IB and check the delegate button). Was working in Ipad simulator because I have 2 different MainWindow xib files, one for iphone/ipod and one for ipad.

Hope this helps someone experiencing a blank screen on startup.