Objective-C exception: CALayerInvalidGeometry

I get this quite often since I work with the picker control (I load data asynchronously, assign it to the picker datasource and so on).

I get this in different cases, sometimes I the error occurs, sometimes not. Any Idea what the problem could be or did anybody have the same problems?

MonoTouch.Foundation.MonoTouchException: Objective-C exception thrown.  Name: CALayerInvalidGeometry Reason: CALayer bounds contains NaN: [0 nan; 320 291]
  at at (wrapper managed-to-native) MonoTouch.ObjCRuntime.Messaging:void_objc_msgSend_int_int_bool (intptr,intptr,int,int,bool)
  at MonoTouch.UIKit.UIPickerView.Select (Int32 row, Int32 component, Boolean animated) [0x00010] in /Developer/MonoTouch/Source/monotouch/src/build/compat/UIKit/UIPickerView.g.cs:185
  at Xamarin.Forms.Platform.iOS.PickerRenderer.UpdatePicker () [0x00000] in <filename unknown>:0
  at Xamarin.Forms.Platform.iOS.PickerRenderer.OnModelSet (Xamarin.Forms.VisualElement model) [0x00000] in <filename unknown>:0
  at Xamarin.Forms.Platform.iOS.ViewRenderer.SetModel (Xamarin.Forms.VisualElement model) [0x00000] in <filename unknown>:0
  at Xamarin.Forms.Platform.iOS.RendererFactory.GetRenderer (Xamarin.Forms.VisualElement view) [0x00000] in <filename unknown>:0
  at Xamarin.Forms.Platform.iOS.ViewPackager.HandleChildAdded (Xamarin.Forms.VisualElement view) [0x00000] in <filename unknown>:0
  at Xamarin.Forms.EnumerableExtensions.ForEach[VisualElement] (IEnumerable`1 enumeration, System.Action`1 action) [0x00000] in <filename unknown>:0
  ....