confirm.php not saving Order Summary data

Hi!
I have been putting a site together for a client who pays commission to her staff when an order is placed by one of their logged in customers.

In order to cope with the possibility of a change in commission rate down the line, I am trying to add a new column to the orders table called Ord_Comm. I currently have the datatype set as FLOAT (the same as the OrderAmount field).

I have added the commission calculation to the form using some basic php maths. The grand total is taken from the e-cart object and the commission rate is taken from a recordset. The calculation in the hidden field on the form displays perfectly.

Now, in the Store Summary in Database behaviour, I have linked my Ord_Comm database field with the 'commission' field in the form on the page, but it will not save the calculated commission rate into the database.

At the same time, there is another column called 'ComPaid_ord' which has a value of '0' added into the Store Summer in Database behaviour and this enters '0' in every time I put a dummy order through.

Any ideas? My client is demonstrating this on Wednesday evenign (UK time) and would greatly appreciate a pointer or two on what's going on...or not!

Many thanks,

Martin