>>>Error building key for index "c:\users\admini~1\appdata\local\temp\000074zt0g0d.cdx" tag "Xyz".
>
>It appears that your index is on a cursor: in the past I experienced issues trying to index a cursor that already has an index on it.
>
>If the purpose is to order your resultset, then do as Tore recommended and use SELECT... ORDER BY rather than indexing the cursor.
>
>Or DELETE TAG ALL before you try to index the cursor.

On readonly cursors you can have one tag, plus any number of side indexes (not the so-called structural indexes, which would go into the same .cdx file, but into a separate file that you need to specify). On readwrite cursors, including SPT, you can index at will.