AutoCAD .NET :: Serialized Custom Object To XRecord Can Not Save DWG

I have polyline that graphically represents a pipe.  Obviously, the polyline can not contain data for a pipe: size, material, insulationtype, insulationthickness, schedule, etc.  So, I have created a custom object with all of the appropriate properties, methods, events, etc that I need for it to behave as a pipe.  My custom object has a reference to the actual polyline with a Handle property stored as a long(since AutoCAD objects can not be serialized).  I referenced an AU 2008 class by Jeffery Geer (A Pattern for Storing Structured Data in AutoCAD Entities CP401-2) to get me as far as I am.

My object is marked serializable.  I serialize it to binary and attach the binary in 127 byte chunks to the xRecord of the polyline object.However, as soon as I attach this binary xrecord, I get the following message when I try to save the drawing:

"One or more objects in this drawing cannot be saved to the specified format.  The operation was not completed and no file was created”