Unknown class pro_exam1ViewController in Interface Builder file.

特郁闷的错误： 我在程序中特意把pro_examviewController删除掉了，为何编译之后运行还是抱这个错误了？
希望大侠能给一个思路，谢谢
[Session started at 2010-10-21 17:10:17 +0800.]
GNU gdb 6.3.50-20050815 (Apple version gdb-1472) (Wed Jul 21 10:53:12 UTC 2010)
Copyright 2004 Free Software Foundation, Inc.
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welcome to change it and/or distribute copies of it under certain conditions.
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This GDB was configured as "x86_64-apple-darwin".sharedlibrary apply-load-rules all
Attaching to process 179.
Pending breakpoint 1 - ""main.m":13" resolved
Pending breakpoint 2 - ""RootViewController.m":17" resolved
Pending breakpoint 3 - ""pro_exam1AppDelegate.m":27" resolved
Current language:  auto; currently objective-c
2010-10-21 17:10:55.229 pro_exam1[179:207] Unknown class pro_exam1ViewController in Interface Builder file.
2010-10-21 17:10:55.277 pro_exam1[179:207] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<pro_exam1AppDelegate 0x5f535d0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key viewController.'
*** Call stack at first throw:
(
0   CoreFoundation                      0x02480b99 __exceptionPreprocess + 185
1   libobjc.A.dylib                     0x025d040e objc_exception_throw + 47
2   CoreFoundation                      0x02480ad1 -[NSException raise] + 17
3   Foundation                          0x0002a0f3 _NSSetUsingKeyValueSetter + 135
4   Foundation                          0x0002a061 -[NSObject(NSKeyValueCoding) setValue:forKey:] + 285
5   UIKit                               0x004a870a -[UIRuntimeOutletConnection connect] + 112
6   CoreFoundation                      0x023f6d0f -[NSArray makeObjectsPerformSelector:] + 239
7   UIKit                               0x004a7121 -[UINib instantiateWithOwner:options:] + 1041
8   UIKit                               0x004a8eb5 -[NSBundle(UINSBundleAdditions) loadNibNamed:owner:options:] + 168
9   UIKit                               0x002b4402 -[UIApplication _loadMainNibFile] + 172
10  UIKit                               0x002b531c -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 198
11  UIKit                               0x002bf3ec -[UIApplication handleEvent:withNewEvent:] + 1958
12  UIKit                               0x002b7b3c -[UIApplication sendEvent:] + 71
13  UIKit                               0x002bc9bf _UIApplicationHandleEvent + 7672
14  GraphicsServices                    0x02d60822 PurpleEventCallback + 1550
15  CoreFoundation                      0x02461ff4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
16  CoreFoundation                      0x023c2807 __CFRunLoopDoSource1 + 215
17  CoreFoundation                      0x023bfa93 __CFRunLoopRun + 979
18  CoreFoundation                      0x023bf350 CFRunLoopRunSpecific + 208
19  CoreFoundation                      0x023bf271 CFRunLoopRunInMode + 97
20  UIKit                               0x002b4c6d -[UIApplication _run] + 625
21  UIKit                               0x002c0af2 UIApplicationMain + 1160
22  pro_exam1                           0x000021d4 main + 102
23  pro_exam1                           0x00002165 start + 53
24  ???                                 0x00000001 0x0 + 1
)
terminate called after throwing an instance of 'NSException'
Program received signal:  “SIGABRT”.