Loading a record on a subform from a combo box - error message

Hi

I'm developing a database for a music shop for a college project.  I have a form setup whereby Customer record is the main form and Order information is the subform. On the customer form I have a combo box which selects the customer record and loads it onto the form. Then obviously all the orders for that customer load in the order subform.

Now in the order subform I want to add an extra level of functionality by having a combo box again, where the user can select an order No and load it onto the subform, rather than having to scroll through the records.  I am using an unbound combo box, and have got the row source to only show records from that customer.

However I can't get the Order No. from the Combo box to load into the Order No. on the subform. I think it may be bacause my Order No. is an auto Number?

Here is the code I am trying to use to make the combo box load the record into my Order subform:

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Private Sub cboFindOrder_AfterUpdate()

Forms![frmShopOrders].Form![frmShopOrdersSubform].SetFocus
Me.Form.RecordsetClone.FindFirst "[OrderNo]='" & Forms![frmShopOrders]![cboFindCustomer] & "'"
If Not Me.Form.RecordsetClone.NoMatch Then
 Me.Form.Bookmark = Me.Form.RecordsetClone.Bookmark
End If

End Sub
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cboFindOrder is my 'find order' combo box.  cboFindCustomer is the combo box on the main form.  The error message I am getting is:

Run time error 3464
Data type mismatch in criteria expression.

I'm thinking this is because Find Customer is a text data type and order no is an autonumber.  However I'm not expereienced enough at VBA to find a solution to this mismatch.  Anyone have any suggestions? I am probably making some fundamanetal error here because Im fairly new to VBA coding and am trying something a bit harder than usual.  the code I used was already off a solution on this forum but am thinking it isnt appropriate for my situation.