Field index out of range

I have been having trouble linking two Paradox 7 tables in D2.
I have set the MasterSource and MasterFIeld properties. The Detail table is
linked to an info power lookup combo box.
When I click on the combo box, I get a 'field index out of range' error.
I have created a secondary index in the detail table. It is of the same
type as the field in the master table. Data is in both tables.
If I try and set the detail table as the mastersource, I get a
'capatability not supported' error.
I have been able to get around linking the tables by using FInkKey and
FieldByName statements,but this is slow and cumbersome.
What am I doing wrong?
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