Prepared Statement - works for SELECT not for UPDATE

I'm connecting to an Access database via ODBC connection. My frontend code is Real Studio (soon to be Xojo).

I'm successfully using a Prepared Statement for the SQL SELECT statement. I'm having all sorts of problems trying to use a Prepared Statement for the SQL UPDATE statement. I'm using the ? as the place holder (works for the SELECT statement) and the UPDATE statement. On executing the UPDATE statement I'm not receiving any database error messages and it appears the update was completed. On checking the table it's not updated. I've checked and double checked that my data correctly matches up with the ? placeholders.

I've posted a thread over at the Real Studio forum regarding this issue though Access is not their primary concern and have only had minimal feedback. That particular thread includes a copy of my code constructing the Prepared Statement. As I mentioned, the SELECT Prepared Statement works, the UPDATE doesn't.

Are there any issues with Prepared Statements and Access? Any suggestions, clues or hints are most welcome.

ps. Access Database is 2003 version, mdb files.