FORALL alias variable already in use: <variable name>

You have a nested ForAll statement inside another ForAll statement and both statements use the same reference variable. Rename one of the variables. For example:

Dim fo(9) As Integer
Dim fee(12) As Integer
Forall x In fo
	Forall x In fee ' error!
	End Forall
End Forall

In this example, you can't use x in the inner loop because it's already used as the reference variable for the outer loop.

You can use the same reference variable name for multiple Forall statements, if they are not nested.