Can’t see how this can be
have you got a single biztalk installation or multiple servers \ hosts?
If not, I would suggest you delete the dll from the gac entirely, restart your host and try running through the biztalk process again. If the program fails then you know you have successfully removed the dll from the system.
If it does not fail its then either the dll is being installed to teh gac but is not visible (not sure this is possible but may be) or there is another host running the old code
Hope this helps
Dino