Code should be like:
INSERT @table(CallID, GroupName, CustPendCase)
Select * from (SELECT '00500588' as CallId,'Desktop' as GroupName,Null as CustPendCase UNION ALL
SELECT '00500588','SD Followup',Null UNION ALL
SELECT '00500600','Server',Null UNION ALL
SELECT '00500600','Service Desk',Null UNION ALL
SELECT...