Hi David,
The indices are strictly based on columns from the same file. However, when I was playing with the query in order to make it work (I ended up converting it to 3 queries in order to get around the join), I crashed on my UPDATE statement for the APP file.

The error I got was "INDEX does not match the table. DELETE the index file AND recreate the index." Even tho the indices are not illegal, there seems to be something seriously wrong. I never had any problems when using strict VFP update commands (REPLACE or working with controlsources) for the APP table.
Thanks for your help.
Shuli