Transact SQL :: Invalid Due To Not Being In Group By Or Aggregate Function

Well adding it to a group by or function skews the result set. How to write this query so it displays as I need it to?  This is what I have thus far, and it works as it should UNTIL I add in the line of 

cast(cte.[C] As float)/cast(sum(cte.[C]) over() as float)*100 As [Rate1],

Presents the error of:
Msg 8120, Level 16, State 1, Line 35
Column 'cte.[C]' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

This is my full on query -- with 3 CTE's involved to get me the actual result set I am after.  

;with cte as
(
select
[state],
case when exists (select 1 from table2 R where R.centername = d.centername) then 1 else 0 end as [L],
case when exists (select 1 from table3 C where C.centername = d.centername) then 1 else 0 end as [C]
FROM maintable d
),

[Code] .....