The style you used to write your query I call "noodles" as it takes to much time to read top understand what you're are doing.

Bit messy, really.

I think the following change should make it work:

SELECT *, dbo.tPeriod.PeriodDiscription, dbo.[tTimeTable2012-13].StaffID, dbo.[tTimeTable2012-13].DayID

FROM dbo.tSubject

INNER JOIN dbo.[tTimeTable2012-13] ON dbo.tSubject.SubjectID = dbo.[tTimeTable2012-13].SubjectID

AND (dbo.[tTimeTable2012-13].StaffID = 18) AND (dbo.[tTimeTable2012-13].DayID = 1)

RIGHT OUTER JOIN dbo.tPeriod ON dbo.[tTimeTable2012-13].PeriodID = dbo.tPeriod.PeriodID

However, I would rewrite it to something like:

SELECT *

FROM dbo.tPeriod AS P

LEFT JOIN dbo.[tTimeTable2012-13] AS T

ON T.PeriodID = P.PeriodID

AND T.StaffID = 18

AND T.DayID = 1

LEFT JOIN dbo.tSubject AS S

ON S.SubjectID = S.SubjectID

Is it easier to see what query is doing now, or am I just too picky?