You may want to check if you have a table with that same name.
other wise, use select idfield from dbf('tablename') where condition.
Because a select statement usually (atleast in vfp6 and below) goes off of the table name and cursors have a temp table name, so that if you don't put the dbf() around the cursor name, the table is not found unless there is an actual table by that name out there.

HTH
Beth