You have to delete 'persistent' connections as well when you disconnect drives:
code:
If InGroup("Test1")
	? "Mapping X:"
	Use X: /Delete /Persistent
	Use X: "\\dusty\1"
	If @Error = 0
		? " Mapping of drive X: Successful"
	Else
		? " Error mapping drive X: to \\dusty\1"
	EndIf
Else
	? " Not in Test1"
EndIf
/Persistent along with /Delete is the keyword

-Erik