Access VBA Can't set focus

Hi

In my Access VBA I run the following code behind a Combo Box and I get the error
"Can't set focus to Customer_Code"
What am I doing wrong?

Private Sub xcmbCustomer_AfterUpdate()

On Error GoTo EH
    '-----------------------------
    Dim oCustomerCode As String
    
    DoCmd.SetWarnings (False)
    
    oCustomerCode = Me.xcmbCustomer.Text
    Me.Customer_Code.SetFocus
    Me.Customer_Code.Text = oCustomerCode
    Call oInsert_New_Invoice_Number 'eg 2018-001
    
    DoCmd.SetWarnings (True)
    '-----------------------------
    Exit Sub
EH:
    MsgBox Err.Description
    
End Sub

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