Select with subquery select not working - sql

Question

I keep getting that error on this code. I am not using EXISTS.Please Help.
Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.
SQL:
If ISDATE(#grpsearch) = 1
SELECT grp.GroupID,
vlanlist.InternetType,
grp.GroupName, cast(grp.StartDateTime as date) as StartDate,
convert(varchar,cast(grp.StartDateTime as time),100) as starttime,
(select case when datepart(hh,convert(datetime,grp.StartDateTime)) > 12 then datepart(hh,convert(datetime,grp.StartDateTime))-12
else case when datepart(hh,convert(datetime,grp.StartDateTime)) = 0 then '12' else datepart(hh,convert(datetime,grp.StartDateTime)) end end as starthour,
datepart(mi,convert(datetime,grp.StartDateTime)) as startmin, case when datepart(hh,convert(datetime,grp.StartDateTime)) >= 12 then 'PM' else 'AM' end as startperiod),
cast(grp.enddatetime as date) as EndDate,
convert(varchar,cast(grp.EndDateTime as time),100) as EndTime,
grp.UserInitials,
grp.UserComments,
roomlist.RoomName,
jacklist.JackNumber
FROM a_Cisco.dbo.grp_internet as grp left outer join
dbo.jacklist as jacklist ON grp.intJack = jacklist.intJack left outer join
dbo.roomlist as roomlist ON grp.intRoom = roomlist.intROom left outer join
dbo.vlanlist as vlanlist ON grp.VlanID = vlanlist.VlanID
WHERE (convert(varchar,cast(grp.StartDateTime as date),100) = #grpsearch)

Answer 1

The problem is this part of the query:
(select case when datepart(hh,convert(datetime,grp.StartDateTime)) > 12
then datepart(hh,convert(datetime,grp.StartDateTime))-12
else case when datepart(hh,convert(datetime,grp.StartDateTime)) = 0
then '12' else datepart(hh,convert(datetime,grp.StartDateTime))
end
end as starthour,
First, you don't need the select at all. Second, you are missing the closing parentheses ()). I would suggest:
(case when datepart(hh,convert(datetime,grp.StartDateTime)) > 12
then datepart(hh,convert(datetime,grp.StartDateTime))-12
else (case when datepart(hh,convert(datetime,grp.StartDateTime)) = 0
then '12'
else datepart(hh,convert(datetime,grp.StartDateTime))
end)
end) as starthour,