Hi all,
I had a closer look at the business transactions available for the transaction control and I am convinced now that the transactions is dependent on the business object type. So, for example 'Change Document' is available for Opportunity and certainly not available for Sales Order.
I am happy to now close the post. The solution would be for me to use the CRM_ORDER_FIELDCHECK Badi to do the control I want.
Cheers!
SF