Maybe a VFP6 reinstall:).

My apps open dbfs with "USE IN 0". Been a while since I last used "Select 0".

USE delme2 in 0 ALIAS a_delme2 ORDER custno1

My seeks also embed the tag

"SET RELATION" ... hmmmmm... I stay away from those "macro" calls. Why not just seek. SET RELATION HAS his own agenda. I don't know how he behaves in every circumstance. Seek is direct - simple and fast.

>Here is the code to recreate!!!! It's kind of long and I'm not sure you need everything but it will fail in VFP 6 SP5. I tested in VFP 8 and it does work.
>
>

>SET SAFETY OFF
>lc_sono   = '        67'
>lc_item   = 'QAD3672        '
>lc_loctid = 'WH1   '
>ln_lineno = 1
>
>CLOSE DATA ALL
>SELECT 0
>CREATE TABLE delme1 (custno C(10), sono C(10), lineno N(4,0))
>
>*-- Add in a bunch of data
>FOR ln_cntr = 65 TO 75
>   FOR i = 1 TO 15
>      INSERT INTO delme1 (custno, sono, lineno) ;
>          VALUES (REPLICATE(CHR(ln_cntr), 4), PADL(ln_cntr, 10), i)
>   ENDFOR
>ENDFOR
>
>*-- Create the index
>INDEX ON DELETED() TAG DELFLAG
>INDEX ON custno TAG custno
>INDEX ON sono   TAG sono
>INDEX ON custno + sono TAG custno1
>INDEX ON sono + STR(lineno, 4) TAG sono1
>USE
>
>USE delme1 ALIAS a_delme1
>SET ORDER TO custno1
>
>SELECT 0
>CREATE TABLE delme2 (item C(15), loctid C(6))
>INSERT INTO delme2 (item, loctid) VALUES (lc_item, lc_loctid)
>INDEX ON DELETED() TAG DELFLAG
>INDEX ON item TAG item
>INDEX ON loctid TAG loctid
>INDEX ON item + loctid TAG item1
>INDEX ON loctid + item TAG loctid1
>USE
>
>USE delme2 ALIAS a_delme2
>SET ORDER TO item1
>
>SELECT 0
>CREATE TABLE delme3 (item C(15))
>INSERT INTO delme3 (item) VALUES (lc_item)
>INDEX ON DELETED() TAG DELFLAG
>INDEX ON ITEM TAG item
>USE
>
>USE delme3 ALIAS a_delme3
>SET ORDER TO ITEM
>
>SELECT 0
>CREATE TABLE delme4 (loctid C(6))
>INSERT INTO delme4 (loctid) VALUES (lc_loctid)
>INDEX ON DELETED() TAG DELFLAG
>INDEX ON loctid TAG loctid
>USE
>
>USE delme4 ALIAS a_delme4
>SET FILTER TO NOT DELETED()
>SET ORDER TO TAG loctid IN a_delme4
>
>SELECT a_delme2
>SET ORDER TO TAG item1 IN a_delme2
>*-- Set relations
>SET RELATION TO item INTO a_delme3, loctid INTO a_delme4
>
>ln_area = SELECT()
>SELECT a_delme2
>lc_order = ORDER("a_delme2")
>SET ORDER TO TAG item1 IN a_delme2
>SEEK lc_item + lc_loctid
>
>? SEEK(lc_sono + STR(ln_lineno, 4), 'a_delme1', 'sono1') && returns .f.
>? SEEK(lc_sono + STR(ln_lineno, 4), 'a_delme1', 'sono1') && returns .t.
>