Do I have to have the receipt number in there twice being it's the primary key?
Code:
myrecset.FindFirst "[ReceiptNumber]=" & Me![ReceiptNumber]
The reference in red represents the field name in the table or query that provides the record source for the form. The reference in green is the name of the control on the form (in your case the combo box that holds the receipt numbers)
...control source for the form is my receipt table.
The receipt table is the record source for the form not the control source.
The control source is where each control (textbox, combo box, list box) on the form gets its data i.e. the control is bound to a field in the record source (the control source property will list a specific field of the table to which the form is bound).
As to the combo box in the header, it must be an unbound control (i.e. the control source property should be blank). Since it is a combo box, it will have a row source (where the data comes from that supplies the combo box with data).
That probably sounds confusing, so the form should be bound to your receipt table (so the receipt table is the record source for the form).
The combo box control in the header is not bound to the record source of the form, and thus the control source property should be blank. But, the row source of the combo box will be your receipt table.