... thinks it's a bound parameter:
select
sessionId
, title
, descr
, byline
, location
, startTime
, endTime
, sortVal
, (SELECT CONVERT(VARCHAR(11), startTime, 106) AS [DD MON YYYY]) as datepart
, (SELECT CONVERT(VARCHAR(11), endTime, 108) AS [hh:mi]) as timepart
from tblSession
order by startTime, sortVal