WWW Crashing on IOS 4.3.3 for unity4

There is an serious bug resulting game crash while loading an AssetBundle by WWW www = new WWW(url) ; We have purchased Unity 4.0 and hope anyone can support us for our project.

The project is build in the Unity 4.0, it runs well on IOS 5.0+, but it crash on IOS 4.3.3 and IOS 4.3.5(compiled with xcode 4.5.1). We have tested with the official AssetBundles example, and the official example also crashed on iOS 4.X version

The error logs as follows:

 terminate called after throwing an instance of 'NSException'
 
 
 
 2012-12-17 17:47:23.442 shootingrpg01[497:607] -[NSURLResponse allHeaderFields]: unrecognized selector sent to instance 0x112e920
 2012-12-17 17:47:23.527 shootingrpg01[497:607] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSURLResponse allHeaderFields]: unrecognized selector sent to instance 0x112e920'
 *** Call stack at first throw:
 (
     0   CoreFoundation                      0x368fd64f __exceptionPreprocess + 114
     1   libobjc.A.dylib                     0x30e1bc5d objc_exception_throw + 24
     2   CoreFoundation                      0x369011bf -[NSObject(NSObject) doesNotRecognizeSelector:] + 102
     3   CoreFoundation                      0x36900649 ___forwarding___ + 508
     4   CoreFoundation                      0x36877180 _CF_forwarding_prep_0 + 48
     5   shootingrpg01                       0x002af79c -[ConnectionDelegate connection:didReceiveResponse:] + 44
     6   Foundation                          0x3422f237 -[NSURLConnection(NSURLConnectionReallyInternal) sendDidReceiveResponse:] + 90
     7   Foundation                          0x3422f13f _NSURLConnectionDidReceiveResponse + 86
     8   CFNetwork                           0x364c657d _ZN19URLConnectionClient29_clientSendDidReceiveResponseEP14_CFURLResponsePNS_26ClientConnectionEventQueueE + 52
     9   CFNetwork                           0x364bbfb5 _ZN19URLConnectionClient26ClientConnectionEventQueue33processAllEventsAndConsumePayloadEP20XConnectionEventInfoI12XClientEvent18XClientEventParamsEl + 212
     10  CFNetwork                           0x364bc0cd _ZN19URLConnectionClient26ClientConnectionEventQueue33processAllEventsAndConsumePayloadEP20XConnectionEventInfoI12XClientEvent18XClientEventParamsEl + 492
     11  CFNetwork                           0x364bbe37 _ZN19URLConnectionClient13processEventsEv + 70
     12  CFNetwork                           0x364bbde9 _ZN13URLConnection24multiplexerClientPerformEP18RunLoopMultiplexer + 36
     13  CFNetwork                           0x364bbd5b _ZN17MultiplexerSource7performEv + 126
     14  CFNetwork                           0x364bbcd9 _ZN17MultiplexerSource8_performEPv + 8
     15  CoreFoundation                      0x368d4a79 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 12
     16  CoreFoundation                      0x368d675f __CFRunLoopDoSources0 + 382
     17  CoreFoundation                      0x368d74eb __CFRunLoopRun + 230
     18  CoreFoundation                      0x36867ec3 CFRunLoopRunSpecific + 230
     19  CoreFoundation                      0x36867dcb CFRunLoopRunInMode + 58
     20  GraphicsServices                    0x3165c41f GSEventRunModal + 114
     21  GraphicsServices                    0x3165c4cb GSEventRun + 62
     22  UIKit                               0x3362bd69 -[UIApplication _run] + 404
     23  UIKit                               0x33629807 UIApplicationMain + 670
     24  shootingrpg01                       0x00005764 main + 160
     25  shootingrpg01                       0x00003a28 start + 40
 )
 terminate called after throwing an instance of 'NSException'
 

This problem is very frustrating, Is there anyway to solve this?

Thanks in advance.