Some times an editor effect will fail to execute and confuse users with only a error message in the log.

This is really confusing to my users here. And I have to go into the python console to fix things up.

I have seen two causes of this:

1) The label image is of an unexpected type, such as uint8, and the effect doesn't support it
2) The label image and primary image have slightly different spacing/origin/orientation

An example of case 1:
$img = sitk.GaborSource(sitk.sitkFloat32)
$sitkUtils.PushForeground(img,"I")
$sitkUtils.PushLabel(img>0,"L")

Load I, and L into editor and the ChangeIslandEffect produces the following error:

ERROR: In /Users/kitware/Dashboards/Nightly/Slicer4/Modules/Scripted/EditorLib/Logic/vtkImageConnectivity.cxx, line 855
vtkImageConnectivity (0x140cb11e0): Warning: Input scalars are type 3 instead of 4

An Example of case 2:
$ img = sitk.GaborSource(sitk.sitkFloat32)
$ sitkUtils.PushForeground(img,"I")
$ l = sitk.Image(img.GetSize(), sitk.sitkInt16)
$ l.CopyInformation(img)
$ l.SetSpacing([img.GetSpacing()[0]+1e-2, img.GetSpacing()[1], img.GetSpacing()[2]])
$ sitkUtils.PushLabel(l,"L2")

Then load I and L2 into the editor. Draw a couple of labels. Running Watersheds from markers produce the following ITK error:
File "/Users/blowekamp/Desktop/Slicer Nightly/Slicer-4.3.1-2013-12-05.app/Contents/lib/Python/lib/python2.7/site-packages/SimpleITK-0.7.1.post1-py2.7-macosx-10.6-x86_64.egg/SimpleITK.py", line 29285, in Execute
return _SimpleITK.MorphologicalWatershedFromMarkersImageFilter_Execute(self, *args)
RuntimeError: Exception thrown in SimpleITK MorphologicalWatershedFromMarkersImageFilter_Execute: /Users/kitware/Dashboards/Nightly/Slicer-build-64bits-QT4.8.5-PythonQt-With-Tcl-CLI-Release-nightly/ITKv4/Modules/Core/Common/include/itkImageToImageFilter.hxx:248:
itk::ERROR: MorphologicalWatershedFromMarkersImageFilter(0x140c24970): Inputs do not occupy the same physical space!
InputImage Spacing: [1.0000000e+00, 1.0000000e+00, 1.0000000e+00], InputImage_1 Spacing: [1.0100000e+00, 1.0000000e+00, 1.0000000e+00]
Tolerance: 1.0000000e-06

This type of change can in info can easily happened when saving to a file type which used test representation of floating point number.

Case 3: Image are different resolutions or regions. I haven't directly tried this recently, but I know some editor effect have segfaulted when the image don't match up.

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RECOMMENDATION
When the label image is loaded, a certain amount of validation should occur. An pop up error should be generated if the image are hopelessly in compatible. If the type is a little off or the meta-data is just a little off the editor should offer to fix those these.