The table has structural index but it has been deleted. The first time table is USEd, VFP throws the error and removes flag that indicates presence of structural index from the header of the table. That allows to open table the second time w/o error.
I would recomend to use new sytuctured error handling TRY...ENDTRY.

>am having this weird problem in our reindex program. following line throwing an error every 2nd time we run our program
>
>use mytable exclu in 0
>
>the error is "Structural .CDX file is not found (Error 1707)"
>
>The issue is no other users in the system and table is not open. cant understand why this error occurs! interestingly the fix to this problem if i try to reopen table in exclusive mode in works fine. i mean like following
>
>on error lberro = .t.
>use mytable exclu in 0
>if lberro
>use mytable exclu in 0
>endif
>
>can any one tell me why this problem occuring ?
>Thanks for your advise