AutoCAD Inventor :: Run-time Error When Creating A WorkPoint?

I have a subroutine which creates a WorkPoint with respect to some adjacent components in an assembly.  As it happens, this subroutine is called twice; once for each of two different instances of a class. The particular snippet within the sub is:

Dim LowerYPt As WorkPoint = Nothing
Try
LowerYPt = AssyCompDef.WorkPoints.AddFixed(TG.CreatePoint(thisX, thisY, thisZ))
Catch ex As Exception
MsgBox(ex.ToString)
End Try

At least one of the X, Y and Z values are different for the two passes.On the first pass, it runs fine.  On the second pass, I get a runtime error:

“System.Runtime.InteropServices.COMException (0x80004005):  Unspecified error (Exception from HRESULT: 0x80004005 (E_FAIL)) at System.RuntimeType……….”