The syntax of the subquery in each day is wrong. You need to construct the subquery for each day like this (Day 6 is the example as it returns a positive result):
Code:
(SELECT tblvagter.label
FROM tblusers INNER JOIN tblvagter ON tblusers.user_id = tblvagter.user_id
WHERE (((Format([start_plan],'dd-mm-yyyy'))='06-04-2006')
AND ((tblvagter.position)="FA"))) AS Day6