"invalid next control variable reference" While trying to compile.

I'm trying to make a Multiple Solver using VBA in excel to make my work go faster.
I cant seem to figure out what i'm doing wrong even tho this should be super simple. (relative new to VBA and Excel)
I think the error has something to do with my "For i" and my "Next i"=?
Hope someone can hlep me out!

PHP Code: 

Sub MultipleSolver()
Dim i As Integer
Dim o As Integer
ActivateWorkbook.ActivateSheet.Activate
For i = 36 To 37
For o = 39 To 51
SolverReset
SolverOk SetCell:="$C$" & i, MaxMinVal:=3, ValueOf:=0, ByChange:="$H$" & o
SolverSolve True
Next i
Next o

End Sub