OK, I have started from scratch and now I am getting an error that the contract ID in the linked table can not be null - which it is not supposed to be.
It seems that it is not getting the value for the inserted record primary key from WADAInsertRecordID
This must be relating to the order that things are happening - the data for the primary table (contracts) is being inserted into the database, but this error pops up when trying to enter the data into the relational (adjoining) table.
Should the insert record primary key be available at this point for the MRT to use?