You are selecting the Start and End dates incorrectly. You do not need to make sub-selects to get these values, as you have already had the tblEmpTaskList JOINed in your query. The resulting query will need to be changed to this:
select stEmpName , stCCodeName , sum(inEffortsInHrs) as hrs ,
sum(inEffortsInMins) as mins, sum(flSec) as s,
max(T.dtTaskDt) as maxdt,
min(T.dtTaskDt) as mindt,
CC.inCCodeID
from
tblEmployeeDetails as E
inner join tblEmpClaimCode as C
on E.inEmpID=C.inEmpID
inner join tblClaimCode as CC
on CC.inCCodeID = C.inCCodeID
inner join tblEmpTaskList as T
on T.inCCodeID = CC.inCCodeID
where E.inEmpID in (@inEmpID) and CC.inCCodeID in (@ClaimCode)
group by CC.inCCodeID , stCCodeName, stEmpName