Updating Checkbox - Run-time Error 91 - Object variable or With block variable not set

Hey,

I have been trying to ensure that one check box is ticked across a row. Each time I select the check box I receive the error "Run-time error 91 - Object variable or With block variable not set".. Please see code below

Option Explicit
Dim CheckBox182  As CheckBox
Dim CheckBox11  As CheckBox
Dim CheckBox12 As CheckBox

Sub CheckBox182_Click()

With Worksheets("02.01.20")
    If CheckBox182.Value = True Then
        CheckBox11.Value = False
        CheckBox12.Value = False
    End If
End With

End Sub
 Sub CheckBox11_Click()
 
  Set CheckBox11 = CheckBox11
    If CheckBox11.Value = True Then
        CheckBox182.Value = False
        CheckBox12.Value = False
    End If
End Sub
Sub CheckBox12_Click()
   
    If CheckBox12.Value = True Then
        CheckBox182.Value = False
        CheckBox11.Value = False
    End If

End Sub

Any help will be appreciated.
Nika