SQL & PL/SQL

I have a query that works in SQL Server but I'm having issues with it in PL/SQL.  I keep running into the error saying "invalid identifier" when I try to reference PlantNumber or Plant_No or any other piece of the CTE or subquery.  Is this not possible with Oracle?

Here's a shortened version of my query:

WITH RemoveData AS
   (
   SELECT a.PLANT_NO,a.ALLOC_WHDV_VOL,a.KW_CTR_REDELIVERED_HV, a.MTR_NO, a.MTR_SFX, a.TRNX_ID, a.REC_STATUS_CD,
MAX(a.ACCT_DT) ACCT_DT
   FROM GasStmt a
   WHERE a.REC_STATUS_CD = 'RR'
   GROUP BY a.PLANT_NO,a.ALLOC_WHDV_VOL,a.KW_CTR_REDELIVERED_HV, a.MTR_NO, a.MTR_SFX, a.TRNX_ID, a.REC_STATUS_CD
   HAVING COUNT(a.REC_STATUS_CD) > 2
   ),
  RemoveData2 AS
   (
   SELECT plant_no "PlantNumber"
   ,SUM(-a.ALLOC_WHDV_VOL) "PlantStandardGrossWellheadMcf"
   ,SUM(KW_CTR_REDELIVERED_HV) "KeepWholeResidueMMBtu"
   FROM RemoveData a
   GROUP BY plant_no
   ),
  OriginalData AS
   (
   SELECT a.PLANT_NO "PlantNumber"
   ,SUM(a.ALLOC_WHDV_VOL) "PlantStandardGrossWellheadMcf"
   ,SUM(CASE WHEN a.REC_STATUS_CD = 'RR' THEN -a.KW_CTR_REDELIVERED_HV ELSE a.KW_CTR_REDELIVERED_HV END) "KeepWholeResidueMMBtu"
   FROM GasStmt a
   LEFT OUTER JOIN (SELECT MTR_NO, MTR_SFX, TRNX_ID, REC_STATUS_CD, MAX(ACCT_DT) ACCT_DT
   FROM GasStmt
   WHERE REC_STATUS_CD = 'RR'
   GROUP BY MTR_NO, MTR_SFX, TRNX_ID, REC_STATUS_CD
   HAVING COUNT(TRNX_ID) > 1) b
   ON a.MTR_NO = b.MTR_NO
   AND a.TRNX_ID = b.TRNX_ID
   AND a.Rec_Status_Cd = b.REC_STATUS_CD
   AND a.Acct_Dt = b.ACCT_DT
   WHERE a.ACCT_DT > '1/1/2010'
   AND b.MTR_NO IS NULL
   GROUP BY a.PLANT_NO
   ),
UnionCTE AS (  
SELECT *
FROM RemoveData2
UNION
SELECT *
FROM OriginalData
)
SELECT PlantNumber, SUM(PlantStandardGrossWellheadMcf) AS PlantStandardGrossWellheadMcf,SUM(KeepWholeResidueMMBtu) AS KeepWholeResidueMMBtu
FROM UnionCTE
GROUP BY PlantNumber

It's the bottom select from UnionCTE that's causing the issue.  Any tips would be appreciated!