"An error occurred while attempting to load this type editor:
Exception has been thrown by the target of an invocation."

I can map it without error through the BO Mapper and I have created several other BO's without problems.  What could cause something like this?

I forgot to mention that if you ever want to test on some code that should on run at design-time, you can use the ReadOnly DesignMode property, like this:

If Me.DesignMode Then

'-- Code that should only run at design-time

End If

Unfortunately, this won't help you in this case, because the DesignMode property will always return False (because it isn't set) until after the constructor exits.  So, once an object has been instantiated, you can test on the property, but until it has been set, you cannot use it. 

Oh, and the property is Protected, so you can only access it within the object (unless you wrap it in a public property).