Hidden Expression Error

I have a parameter with multiple values .

So I have a task where if  user selects multiple values  from the parameter the textbox must be visible or else it should not be visible. I am getting following error when writing this expression

=IIF( (Parameters!Type.value= "SENIOR")AND (Parameters!Type.Value="COMMERCIAL"),TRUE,FALSE)

The Hidden Expression for the Text Box contains Error: Overload resolution failed because no public '=' can be called with these arguments etc..                Pls Help what kind of expression I had to use. Thank You..:)