Very often when I try to edit UILabels in storyboard, Xcode is crashing. Any ideas what could be causing this? It looks like it has something to do with one of the autolayout constraints. Here's the error report:

```
Process:         Xcode [43938]
Path:            /Applications/Xcode.app/Contents/MacOS/Xcode
Identifier:      com.apple.dt.Xcode
Version:         4.5 (1839)
Build Info:      IDEApplication-1839000000000000~3
App Item ID:     497799835
App External ID: 10747437
Code Type:       X86-64 (Native)
Parent Process:  launchd [43283]

Date/Time:       2012-10-01 09:43:36.443 -0400
OS Version:      Mac OS X 10.7.4 (11E53)
Report Version:  9
Sleep/Wake UUID: 8C7C93A7-0BEF-42C6-944C-488D8C7896DD

Interval Since Last Report:          152594 sec
Crashes Since Last Report:           6
Per-App Interval Since Last Report:  135715 sec
Per-App Crashes Since Last Report:   5
Anonymous UUID:                      E745D8FE-362B-4FD2-8594-7EC5C26767B2

Crashed Thread:  0  Dispatch queue: com.apple.main-thread

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000

Application Specific Information:
ProductBuildVersion: 4G182
ASSERTION FAILURE in /SourceCache/IDEInterfaceBuilderCocoaTouch/IDEInterfaceBuilderCocoaTouch-1926/IBPlugin/Utilities/IBObjectMarshalling.m:651
Details:  Failed to start deciding frames for IBNSLayoutConstraint, IBUILabel, IBUITabBarItem, IBUITableView, IBUIView, and IBUIViewController.

Interface Builder encountered an error communicating with the iOS Simulator. If you choose to file a crash report or radar for this issue, please check Console.app for crash reports for "Interface Builder Cocoa Touch Tool" and include their content in your crash report.

Exception name: IBAssertionFailure
Exception reason: ASSERTION FAILURE: realConstraint
Reason:     Should have found real constraint for represented constraint <NSLayoutConstraint:0x86a8c30 H:[UIView:0x868a0f0(71)]>
File:       /SourceCache/IBAutolayoutFoundationIOS/IBAutolayoutFoundation-1818/Framework/Classes/Arbitration/IBAutolayoutEngine.m:223
Method:     __76-[IBAutolayoutEngine realConstraintsFromCollectionOfRepresentedConstraints:]_block_invoke_0
Exception backtrace: 
  0. CoreFoundation           0x022a4012 __exceptionPreprocess
  1. libobjc.A.dylib          0x01703e7e objc_exception_throw
  2. CoreFoundation           0x0232cfb1 -[NSException raise]
  3. ???                      0x0000beae [IBCocoaTouchTool startAutolayoutFrameDecisionSessionWithRequest:document:]
  4. ???                      0x000342a5 [IBMessageReceiveChannel deliverMessage:toTarget:withArguments:result:]
  5. ???                      0x00033fa9 [IBMessageReceiveChannel deliverMessage:toTarget:withArguments:result:]
  6. ???                      0x00033c47 [IBMessageReceiveChannel runBlockingReceiveLoopNotifyingQueue:notifyingTarget:]
  7. libdispatch.dylib        0x04c3d731 _dispatch_barrier_sync_f_slow_invoke
  8. libdispatch.dylib        0x04c4c014 _dispatch_client_callout
  9. libdispatch.dylib        0x04c3c7d5 _dispatch_main_queue_callback_4CF
 10. CoreFoundation           0x0224aaf5 __CFRunLoopRun
 11. CoreFoundation           0x02249f44 CFRunLoopRunSpecific
 12. CoreFoundation           0x02249e1b CFRunLoopRunInMode
 13. Foundation               0x01308c7c -[NSRunLoop(NSRunLoop) runMode:beforeDate:]
 14. ???                      0x0000cf06 [IBCocoaTouchTool startServingReceiveChannel:]
 15. ???                      0x0000d09f [IBCocoaTouchTool startServingWithSocket:]
 16. ???                      0x0000e1b7 [IBCocoaTouchTool .cxx_destruct]
 17. ???                      0x00002365 ???
Exception info:{
}

```