I have a taxlot that is giving me troubles in a Union. When I try to run the union I get the tried and true ''Geometry is not M-Aware'' message. (there are no Polygon-M features). Based on readings on this site and the ESRI forums, I'm now trying to explode my taxlots prior to the union. However I seem to have come across a mystical indestructible shape. I've tried check and repair geometry with no results. I've tried the Multipart-to-Singlepart tool and receive this message:
Cannot process feature with OID ...
Failed to execute
So I tried the explode function in the Advanced Editing Toolbar and go this lovely message:

I calculated (!SHAPE!.partCount) the number of parts into a field and came up with 22.
Here is what the shape looks like:
Help?