Are you using non-structural indexes? What for?

>VFP 9.2
>
>Hi,
>
>I am facing an error while updating :
>
>BEGIN TRANSACTION
>Error 1548
>Table myTable has one or more non-structural indexes open. Please close them and Retry the begin Transaction
>Line 50
>UpdateRows
>
>How can I check which non-structural index is open and how to close that one?
>
>
>Regards,
>
>Koen