Method Range of object worksheet failed

I have a multiple sheet Excel sheet and i've included a calendar function to easily change the date of birth using this Explicit option on sheet 6
(Codes on sheet 6)

Option Explicit


Private Sub Worksheet_SelectionChange(ByVal Target As Range)

Dim isect As Range
If Target.Cells.Count > 1 Then Exit Sub

Set isect = Intersect(Target, Range("$E$3,$E$5,$G$3:$G$5"))
If Not isect Is Nothing Then
frmCalendar.Show_Cal
End If
End Sub

When I try to use the solver (with VBA code) on this sheet, i receive this error

Method Range of object worksheet failed

If I use the solver on any other sheets, it runs well

In Module 1 the codes for the solver is
(Button in sheet 6 calling macro in module 1)

Sub OptimisingPay()
'
'
    SolverReset
    SolverOk SetCell:="$w$4", MaxMinVal:=3, ValueOf:="0", ByChange:="$w$3"
    SolverSolve UserFinish:=True
    SolverReset
    SolverOk SetCell:="$x$4", MaxMinVal:=3, ValueOf:="0", ByChange:="$x$3"
    SolverSolve UserFinish:=True
    SolverReset
    Range("M23").Value = Range("W3")
    Range("N23").Value = Range("X3")
    
End Sub

Is there a way to correct this?
Many thanks