ERROR : Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

hi anyone help me.. what is wrong in may query.. heres my query..
SELECT DISTINCT  (CASE T.urgency WHEN 'Urgent'  THEN 'High'  WHEN 'Medium' THEN 'Medium' WHEN 'Low' THEN 'Low'  END) as Urgency, T.ticket_id, (CASE T.subject WHEN '' THEN T.subclass ELSE T.subject END) AS subject, (SUBSTRING(T.[content],0,100) + '..') as content, ('by ' + (SELECT firstname FROM tblusers WHERE userid = T.postby) + ' / ' + CONVERT(VARCHAR(50), T.postdate)) as postbydt, T.confirmation, + (CASE status WHEN 'closed' THEN 'Closed' ELSE (CASE WHEN lockedby IS NOT NULL THEN 'locked' ELSE (CASE confirmation WHEN '1' THEN 'Completed' WHEN '4' THEN 'Support Reply' WHEN '5' THEN 'User Reply' WHEN '0' THEN 'New' END) END) END) AS status, (CASE WHEN ((SELECT TOP 1 R.postdate FROM tblReplies AS R WHERE (R.deleted IS NULL OR R.deleted = 0) AND R.ticket_id = T.ticket_id) IS NOT NULL AND (SELECT TOP 1 C.postdate FROM tblComments AS C WHERE (C.deleted IS NULL OR C.deleted = 0) AND C.t ...