title: Xcode keeps crashing
body: <p>I just started out programming for iOS. I tried adding an enter button for a simple calculator and changing its size, but Xcode keeps crashing. This is the report:</p>
  
  <pre><code>Process:         Xcode [406]
  Path:            /Applications/Xcode.app/Contents/MacOS/Xcode
  Identifier:      com.apple.dt.Xcode
  Version:         4.5.1 (1842)
  
  Crashed Thread:  0  Dispatch queue: com.apple.main-thread
  
  Exception Type:  EXC_CRASH (SIGABRT)
  Exception Codes: 0x0000000000000000, 0x0000000000000000
  
  Application Specific Information:
  ProductBuildVersion: 4G1004
  ASSERTION FAILURE in /SourceCache/IDEInterfaceBuilderCocoaTouch/IDEInterfaceBuilderCocoaTouch-1929/IBPlugin/Utilities/IBObjectMarshalling.m:651
  Details:  Failed to arbitrate IBNSLayoutConstraint, IBUIButton, IBUILabel, 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: 
  Reason:     All views needing candidate constraints have already had constraints generated. This most likely indicates a bug involving layout of the following views:
      Layout engine frame ({{20, 20}, {282, 36}}) of &lt;UILabel: 0x81f5560; frame = (20 20; 281 36); text = '0'; clipsToBounds = YES; opaque = NO; autoresize = TM+BM; userInteractionEnabled = NO; layer = &lt;CALayer: 0x815cdd0&gt;&gt; does not match canvas frame ({{20, 20}, {281, 36}})
  </code></pre>
  
  <p>I've already tried reinstalling Xcode and resetting iOS simulator as well. I have Mountain Lion.</p>