I have the following query and I am calling UDF defined function.  But
when i runuit it gives me following error message

Msg 229, Level 14, State 5, Line 1
EXECUTE permission denied on object 'TimeDifference', database
'twcsan', owner 'dbo'.

SELECT
tck.tcktreceived,
tck.ticketid,
tckmsg.tcktmessage,
dbo.TimeDifference(tck.tcktreceived, GETDATE())
FROM tbtickets AS tck
INNER JOIN tbticketsmessages AS tckmsg ON tck.ticketid =
tckmsg.ticketid