ERROR:Subquery returned more than 1 value.Please help me

hi karthik, error reason is clear that you assigning more than 1 record to @Signeddate n thats not allowed.......

but their is 1 solution for your above logic...if  i am not wrong ..you are going to update every record of #TEMP_SB according to SCHEDULEDTIME....if so then you have to excute your above logic for every row of #TEMP_SB  in while loop like below......
for that modify your #TEMP_SB  and add 1 more column of rownumer starting from zero(0) using RowNumber() function of sql server .......n execute you code in while loop...i modified your code...you will get idea from it

DECLARE @Expiration DATETIME;
DECLARE @Signeddate VARCHAR(50);
DECLARE @TextMarketing VARCHAR(50);
declare @Count int;
declare @rownum int;
set @rownum=0;

  select @Count =(SELECT Count(SCHEDULEDTIME) FROM #TEMP_SB );
 
  while @rownum<@count
  begin
   Select @Signeddate=(SELECT SCHEDULEDTIME FROM #TEMP_SB where rownumber=@rownum; --this will give  one record at a time
        SET @Expiration=(DATEADD(DAY,-1,(DATEADD(YEAR,1,@Signeddate))))
         If(@Signeddate<=@Expiration)
          BEGIN
       SET @TextMarketing='ACTIVE';
         END
 else if(@Expiration is not null OR @Expiration < GETDATE())
  BEGIN
      SET @TextMarketing='INACTIVE';
  END
 UPDATE  #TEMP_SB SET TEXT_MARKETING_STATUS=@TextMarketing

      @rownum=@rownum+1;

  end