VBA code does not add a constraint from solver

[goncalogera]

I've encountered a problem while trying to add a solver function to a userform button.

The solver is running well with the exception that it's not adding a specific constraint. The code for the solver is as follows:

Sub Solver1()
    SolverReset
    SolverOk SetCell:="$I$12", MaxMinVal:=2, ByChange:="$K$2:$K$7", _
        Engine:=1, EngineDesc:="GRG Nonlinear"
    SolverAdd CellRef:="$J$12", Relation:=2, FormulaText:="1"
    SolverAdd CellRef:="$K$2:$K$7", Relation:=5, FormulaText:="binary"
    SolverAdd CellRef:="$L$2:$L$7", Relation:=3, FormulaText:="0"
    SolverSolve userfinish:=True
End Sub

Cell $J$12 is a SUM of cells $K$2:$K$7 which are all the binary constraints.

Since it's a MIN objective solver only one can be equal to 1 and there always has to be a restraint equal to one hence the need of a binary constraint and the one which is not working which is the SUM of all binaries. That constraint has to be binary since this is an optimization problem where the variables are 0 if not chosen and 1 if chosen.

I've seen threads where they suggest using to SolverSolve lines twice but it doesn't work.

The userform button code is as follows:

Private Sub CalculateButton_Click()
    Dim sh As Worksheet
    Set sh = ThisWorkbook.Sheets("Spreads")

    sh.Range("K12").Value = Me.MontanteBox.Value
    sh.Range("M12").Value = Me.txtStartDate.Value
    sh.Range("N12").Value = Me.txtDueDate.Value

    Call Module3.Solver1

    If sh.Range("K2") = 1 Then
        MsgBox "Escolha ótima será o Novo Banco", vbInformation
        Exit Sub
    End If

    If sh.Range("K3") = 1 Then
        MsgBox "Escolha ótima será o BCP", vbInformation
        Exit Sub
    End If

    If sh.Range("K4") = 1 Then
        MsgBox "Escolha ótima será o BIC", vbInformation
        Exit Sub
    End If

    If sh.Range("K5") = 1 Then
        MsgBox "Escolha ótima será a CGD", vbInformation
        Exit Sub
    End If

    If sh.Range("K6") = 1 Then
        MsgBox "Escolha ótima será o BPI", vbInformation
        Exit Sub
    End If

    If sh.Range("K7") = 1 Then
        MsgBox "Escolha ótima será o DB", vbInformation
        Exit Sub
    End If
End Sub

Thanks for your help in advance!