Bizarre key-value coding error for basic UILabel - objective-c

Question

This is a new one. I'm testing that my various viewcontrollers are getting loaded by my tab bar, so I put this on one of them:
- (void)viewDidLoad
{
[super viewDidLoad];
UILabel*yo=[[UILabel alloc] init];
self.testlabel=yo;
self.testlabel.text=[NSString stringWithFormat:#"sup"];
[yo release];
This is what I get when I click the tab button for that controller:
2011-07-26 14:05:37.773 Pickers[802:707] Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key testlabel.'*
What in the world?! I must be doing something exceptionally basic and wrong here. Can anyone spot it?
I've got this in the .h and .m:
#interface SingleVC : UIViewController
#property (nonatomic, retain) IBOutlet UILabel*testlabel;
#end
and
#implementation SingleVC
#synthesize testlabel;
I get the following stack errors (which I do not know how to read):
*** Call stack at first throw:
(
0 CoreFoundation 0x00dc25a9 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x00f16313 objc_exception_throw + 44
2 CoreFoundation 0x00dc24e1 -[NSException raise] + 17
3 Foundation 0x00794677 _NSSetUsingKeyValueSetter + 135
4 Foundation 0x007945e5 -[NSObject(NSKeyValueCoding) setValue:forKey:] + 285
5 UIKit 0x0021030c -[UIRuntimeOutletConnection connect] + 112
6 CoreFoundation 0x00d388cf -[NSArray makeObjectsPerformSelector:] + 239
7 UIKit 0x0020ed23 -[UINib instantiateWithOwner:options:] + 1041
8 UIKit 0x00210ab7 -[NSBundle(UINSBundleAdditions) loadNibNamed:owner:options:] + 168
9 UIKit 0x000c6628 -[UIViewController _loadViewFromNibNamed:bundle:] + 70
10 UIKit 0x000c4134 -[UIViewController loadView] + 120
11 UIKit 0x000c400e -[UIViewController view] + 56
12 UIKit 0x000d6f54 -[UITabBarController transitionFromViewController:toViewController:transition:shouldSetSelected:] + 120
13 UIKit 0x000d5aaa -[UITabBarController transitionFromViewController:toViewController:] + 64
14 UIKit 0x000d78a2 -[UITabBarController _setSelectedViewController:] + 263
15 UIKit 0x000d7711 -[UITabBarController _tabBarItemClicked:] + 352
16 UIKit 0x000144fd -[UIApplication sendAction:to:from:forEvent:] + 119
17 UIKit 0x00216ce6 -[UITabBar _sendAction:withEvent:] + 422
18 UIKit 0x000144fd -[UIApplication sendAction:to:from:forEvent:] + 119
19 UIKit 0x000a4799 -[UIControl sendAction:to:forEvent:] + 67
20 UIKit 0x000a6c2b -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
21 UIKit 0x000a4750 -[UIControl sendActionsForControlEvents:] + 49
22 UIKit 0x000144fd -[UIApplication sendAction:to:from:forEvent:] + 119
23 UIKit 0x000a4799 -[UIControl sendAction:to:forEvent:] + 67
24 UIKit 0x000a6c2b -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
25 UIKit 0x000a57d8 -[UIControl touchesEnded:withEvent:] + 458
26 UIKit 0x00038ded -[UIWindow _sendTouchesForEvent:] + 567
27 UIKit 0x00019c37 -[UIApplication sendEvent:] + 447
28 UIKit 0x0001ef2e _UIApplicationHandleEvent + 7576
29 GraphicsServices 0x00ffb992 PurpleEventCallback + 1550
30 CoreFoundation 0x00da3944 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
31 CoreFoundation 0x00d03cf7 __CFRunLoopDoSource1 + 215
32 CoreFoundation 0x00d00f83 __CFRunLoopRun + 979
33 CoreFoundation 0x00d00840 CFRunLoopRunSpecific + 208
34 CoreFoundation 0x00d00761 CFRunLoopRunInMode + 97
35 GraphicsServices 0x00ffa1c4 GSEventRunModal + 217
36 GraphicsServices 0x00ffa289 GSEventRun + 115
37 UIKit 0x00022c93 UIApplicationMain + 1160
38 Pickers 0x000025c9 main + 121
39 Pickers 0x00002545 start + 53
)
terminate called throwing an exceptionCurrent language: auto; currently objective-c
kill
quit

Answer 1

So after some Googling on other sites, it turns out that quite a few people have had this exact same and basic problem. I found the solution here:
https://discussions.apple.com/thread/1598422?threadID=1598422
I was checking my classes within the individual nibs of each controller, but you must also set the classes in the tab controller as well, for each item (I had already set the nib name for each tab bar item, but not the class).
so, problem resolved and was, as expected, quite basic.
It's a stumper why the error created was for key value coding, though.

Answer 2

perhaps a connection in IB from some object that formerly had an IBOutlet called testlabel?
stop the debugger in ObjC Exceptions and post your stack trace if it's not obvious