error from varchar to bigint

yesterday i put a piece together for a summation, worked just fine.  today i tried to add one more sum into it, and it keeps failing with msg 8114 -- error converting data type varchar to bigint.  here is the proc before my change:
SELECT
      Symbol,
      EndPoint,
      'Add'=LEFT(CONVERT(VARCHAR(20),CAST(SUM(Adds) AS MONEY), 1),LEN(CONVERT(VARCHAR(20),CAST(SUM(Adds) AS MONEY), 1)) - 3),
      'Remove'=LEFT(CONVERT(VARCHAR(20),CAST(SUM(Remove) AS MONEY), 1),LEN(CONVERT(VARCHAR(20),CAST(SUM(Remove) AS MONEY), 1)) - 3),      
      Volume
FROM (
SELECT
      Symbol,
      EndPoint,
      SUM(CASE WHEN lflag IN ('A','17','18','25','26','27','28','43','44') THEN quantity ELSE 0 END) AS 'Adds',
      SUM(CASE WHEN lflag IN ('R','N','02','21','22','24') THEN quantity ELSE 0 END) AS 'Remove',
      LEFT(CONVERT(VARCHAR(20), CAST(SUM(quantity) AS MONEY), 1),LEN(CONVERT(VARCHAR(20),CAST(SUM(quantity) AS MONEY), 1)) - 3)  AS Volume
FROM
      ......... t WITH (NOLOCK)
WHERE
      blah blah blah
GROUP BY
      Symbol,
      EndPoint ) ev
GROUP BY
      Symbol,
      EndPoint,
      Volume

UNION ALL

SELECT
      Symbol,
      ' ' AS EndPoint,
      ' ' AS 'Add',
      ' ' AS 'Remove',
      ' ' AS 'Volume'
FROM
      ........... WITH (NOLOCK)
WHERE
      blah blah blah.....
GROUP BY
      Symbol
ORDER BY       
      Symbol,
      EndPoint,
      Volume

this is a sample result:

symbol          endpoint        adds         remove                volume
EWJ                        
EWJ      AAAA      77,411      0      77,411
EWJ      BBBB      34,190      3,300      37,490
SIRI                        
SIRI      AAAA      30,400      14,100      44,500
SIRI      BBBB      45,100      29,400      80,400

i am trying to change it to total that volume on the far right -- on the top of each distinct symbol line, like this:

EWJ                                      114,901
EWJ      AAAA      77,411      0      77,411
EWJ      BBBB      34,190      3,300      37,490
SIRI                                      124,900
SIRI      AAAA      30,400      14,100      44,500
SIRI      BBBB      45,100      29,400      80,400


i tried adding this to that bottom select --
(SUM(CASE WHEN lflag IN ('A','17','18','25','26','27','28','43','44') THEN quantity ELSE 0 END) +
SUM(CASE WHEN lflag IN ('R','N','02','21','22','24') THEN quantity ELSE 0 END)) AS 'Volume'

it works by itself, but it fails when i try to run the whole piece together --- the upper unioned to the lower.