Try this instead:

If T_Zone > 0 Then
Low P_Zone1 : Low P_Zone2.........and so on.....
Select Case current_zone
Case 1
High P_Zone1
Case 2
High P_Zone2
...................................and so on.....
End Select
Endif



And what pin is P_Zone17 on?
For that matter, seeing all the code might not be a bad idea.