Format As Text In Append Query

I have some code that creates a dynamic "Append To" query. The problem is that when the code is run it creates the query but generates a Data Type Mismatch error. I have tracked this down to a [clientnumber] field which is formatted as text in both the main database and the one the Append to query is updating.

The client number appears as a criteria and this works for finding the client's record but it will not append it unless I enclose it in quotes. When it's in quotes it works fine.

Can anybody give me a clue as to how I can include, in the code, a formatting command that makes the information inserted into the criteria field appear enclosed in quotes. Or-

Perhaps explain why the problem exists when both fields are formatted the same in both the main table and the Appended To table.

thanks