VBA Error Run-Time 91 - object variable or with block variable not set (Duplicate)

Hi, I'm having trouble with a line in my code, it compiles...
but whenever I run it I get a #91 error
The code is supposed to identify duplicates in a field.

Function ValidateEntries() As Boolean
    
    ValidateEntries = True
    
    Dim iPVNr As Variant
    Dim sh As Worksheet
    iPVNr = frmForm.txtPVnr.Value
    
    With frmForm
        
        '~~> Default colors for mandatory fields
        .txtPVnr.BackColor = vbWhite
        .txtDatum.BackColor = vbWhite
        .cmbPost.BackColor = vbWhite
        .cmbLocatie.BackColor = vbWhite
        .cmbOvertreding.BackColor = vbWhite
        .cmbBevinding.BackColor = vbWhite
        .cmbOpslagplaats.BackColor = vbWhite
        .cmbVerbalisant1.BackColor = vbWhite
        .txtOpmerking.BackColor = vbWhite
        '----------------------------------------------------------------------
        
        If Trim(.txtPVnr.Value) = "" Then
        
            MsgBox "Please enter PV nr.!", vbOKOnly + vbInformation, "PVnr"
            ValidateEntries = False
            .txtPVnr.BackColor = vbRed
            .txtPVnr.SetFocus
            Exit Function
            
        End If
        
        '~~> Validating Duplicate entries
        If Not sh.Range("B:B").Find(what:=iPVNr, lookat:=xlWhole) Is Nothing Then
        
            MsgBox "Duplicate PV nr. found!", vbOKOnly + vbInformation, "PVnr"
            ValidateEntries = False
            .txtPVnr.BackColor = vbRed
            .txtPVnr.SetFocus
            Exit Function
                    
        End If