The error still occurs not sure what to do here!
In a previouse post, you said that its best to target 2.0, with the 8.1 is it safe to target the 4.0 framework?
See refrence below:
http://www.kinook.com/Forum/showthread.php?t=4987
If 4.0 is supported I can try doing that and see if it handles interop's differntly.