SOLVED :)
SELECT a.Month, a.MonthLabel, COUNT (a.ID) AS aCount
FROM
(
SELECT admin.ID, dimDate.Month, dimDate.MonthLabel
FROM admin
INNER JOIN dimDate ON (dimDate.keyDate >= admin.sDate AND dimDate.keyDate <= admin.eDate) OR (dimDate.keyDate >= admin.sDate AND admin.eDate Is Null)
GROUP BY...