After hitting my head on my desk, cursing in my mind (cubicles aren't very private) and wanting to chuck my computer through the window, I figured it out.
This probably won't work for everyone, but it could be a good starting point. In my codebehind I had a SizeChanged declared.
this.SizeChanged += new SizeChangedEventHandler(myControl_SizeChanger);
Once I commented out (and then got rid of) the size changed event, the error went away.
to get the autosizing I wanted on this control, in the main "header" (that's what I call the code at the top that declares all of the xmlns values), I set a DESIGN height and width instead of simply stating Height and Width :
mc:Ignorable="d" d:DesignHeight="100" d:DesignWidth="100">
.... rest of code here