Improvement found:

I took this first subquery out and turned it into a function:

  (select count(meetingnumber) from dbo.meetings
	where (begintime between det.StartTime and dateadd(mi,@iLength,det.StartTime)
        or     endtime   between det.StartTime and dateadd(mi,@iLength,det.StartTime)
        	or det.StartTime between begintime and endtime
        	or dateadd(mi,@ilength,det.StartTime) between begintime and endtime)
        	and iscancelled=0 and roomid = det.RoomID ) as RoomConflict,

and called the function instead and it works again.

Kirk