Trying to pull distinct IDs

I am trying to pull a list of distinct IDs based on maximum ContEnd_Switch date. If I change the ContEnd_Switch in the select statement to a MAX(ContEnd_Switch) and then take out the ContEnd_Switch in the Group by clause, then it won't work because I need a group by because I have ContEnd_Switch in the Order by clause. If I add Max(ContEnd_Switch) to the Having clause, for example Having Max(ContEnd_Switch) = ContEnd_Switch, then this will not work either because there are rows in the data with null ContEnd_Switch dates. Please help!

SELECT ProspectID, Prospect, ContEnd_Switch, TargetPrice, SUM(MwhAct * Total) / SUM(MwhAct) AS WAverage, 
                                GM_MarRate, Comm_1_Rate, Comm_2_Rate, Comm_3_Rate, Comm_4_Rate, Comm_5_Rate, Comm_6_Rate 
                FROM Prospect_Cogs 
                WHERE (Fwd_Mth BETWEEN 1 AND 12) and SRID = 176 and (Realtime in (select Realtime from tbl_realtime) ) 
                GROUP BY ProspectID, Prospect, TargetPrice, ContEnd_Switch, GM_MarRate, Comm_1_Rate, Comm_2_Rate, Comm_3_Rate, Comm_4_Rate, Comm_5_Rate, Comm_6_Rate 
                having SUM(MwhAct * Total) / SUM(MwhAct) > 0
                order by CASE 0
                                          when 1 then cast(ContEnd_Switch as varchar)  -- by end contract  
                                          when 2 then cast(TargetPrice as varchar)   -- Target Price 
                                          when 3 then cast(SUM(MwhAct * Total) / SUM(MwhAct) as varchar) --by quoted Price
                                          else Prospect    --by Prospect Name 
                                 END

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