Never mind. Try this:
SELECT @retvalOUT = CONVERT(TINYINT,x.OutputColumn)
FROM [dbo].[SLADCSchedule]
CROSS APPLY (
SELECT OutputColumn =
CASE @DayOfWeek
WHEN 1 THEN Sunday
WHEN 2 THEN Monday
WHEN 3 THEN Tuesday
WHEN 4 THEN Wednesday
WHEN 5 THEN Thursday
WHEN 6 THEN Friday
WHEN 7 THEN Saturday
END
) x
WHERE ScheduleStart <= @OrderEntryDate
AND ScheduleEnd >= @OrderEntryDate
AND BranchID = 99
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden