Error when using ROW_COUNT alias in where clause

SELECT DISTINCT 
                         dbo.AUDIT_TRAIL.SOURCE_TABLE, dbo.AUDIT_TRAIL.SOURCE_AK, dbo.AUDIT_TRAIL.SOURCE_FIELD, dbo.AUDIT_TRAIL.ORIG_VALUE, 
                         dbo.AUDIT_TRAIL.NEW_VALUE, dbo.BA_VIEW_SHIPPING_ORDERS.ENTRY_DATE AS SHIP_ENTRY_DATE, dbo.AUDIT_TRAIL.STAMPTIME, 
                         dbo.BA_VIEW_SHIPPING_ORDERS.SM_NUMBER, dbo.SYS_USERS.USER_NAME, dbo.SYS_USERS.FIRST_NAME, dbo.SYS_USERS.LAST_NAME, 
                         dbo.VIEW_SM_STOCK.STM_AUTO_KEY, dbo.VIEW_SM_STOCK.QTY_RESERVED, dbo.VIEW_SM_STOCK.QTY_SHIPPED, dbo.VIEW_SM_STOCK.STOCK_LINE, 
                         dbo.VIEW_SM_STOCK.CONDITION_CODE, dbo.VIEW_SM_STOCK.WAREHOUSE_CODE, dbo.VIEW_SM_STOCK.ORIG_WAREHOUSE_CODE, 
                         dbo.VIEW_SM_STOCK.LOCATION_CODE, dbo.VIEW_SM_STOCK.SERIAL_NUMBER, dbo.SYS_USERS.EMPLOYEE_CODE,
						 ROW_NUMBER() OVER(PARTITION BY BA_VIEW_SHIPPING_ORDERS.SM_NUMBER,AUDIT_TRAIL.SOURCE_AK ORDER BY VIEW_SM_STOCK.STM_AUTO_KEY DESC) AS RN
FROM            dbo.VIEW_SM_STOCK RIGHT OUTER JOIN
                         dbo.BA_VIEW_SHIPPING_ORDERS ON dbo.VIEW_SM_STOCK.SMD_AUTO_KEY = dbo.BA_VIEW_SHIPPING_ORDERS.SMD_AUTO_KEY LEFT OUTER JOIN
                         dbo.AUDIT_TRAIL LEFT OUTER JOIN
                         dbo.SYS_USERS ON dbo.AUDIT_TRAIL.SYSUR_AUTO_KEY = dbo.SYS_USERS.SYSUR_AUTO_KEY ON 
                         dbo.BA_VIEW_SHIPPING_ORDERS.SMH_AUTO_KEY = dbo.AUDIT_TRAIL.SOURCE_AK						 
WHERE        (dbo.AUDIT_TRAIL.SOURCE_TABLE = 'SMH') AND (dbo.AUDIT_TRAIL.ORIG_VALUE = 'PICKING') AND (dbo.AUDIT_TRAIL.NEW_VALUE = 'PACKING') OR RN = '1' 
GROUP BY dbo.AUDIT_TRAIL.SOURCE_AK, dbo.VIEW_SM_STOCK.STM_AUTO_KEY, dbo.AUDIT_TRAIL.SOURCE_TABLE, dbo.AUDIT_TRAIL.SOURCE_FIELD, dbo.AUDIT_TRAIL.ORIG_VALUE, 
                         dbo.AUDIT_TRAIL.NEW_VALUE, dbo.BA_VIEW_SHIPPING_ORDERS.ENTRY_DATE, dbo.AUDIT_TRAIL.STAMPTIME, dbo.BA_VIEW_SHIPPING_ORDERS.SM_NUMBER, 
                         dbo.SYS_USERS.USER_NAME, dbo.SYS_USERS.FIRST_NAME, dbo.SYS_USERS.LAST_NAME, 
                         dbo.VIEW_SM_STOCK.QTY_RESERVED, dbo.VIEW_SM_STOCK.QTY_SHIPPED, dbo.VIEW_SM_STOCK.STOCK_LINE, dbo.VIEW_SM_STOCK.CONDITION_CODE, 
                         dbo.VIEW_SM_STOCK.WAREHOUSE_CODE, dbo.VIEW_SM_STOCK.ORIG_WAREHOUSE_CODE, dbo.VIEW_SM_STOCK.LOCATION_CODE, 
                         dbo.VIEW_SM_STOCK.SERIAL_NUMBER, dbo.SYS_USERS.EMPLOYEE_CODE
ORDER BY SOURCE_AK