列的类型与UNPIVOT列表中指定的其他列的类型冲突

Question

SELECT 
   RMS_Code, Property, Value
FROM
    (SELECT 
         RMS_Code, 
         ITEM_CODE= CONVERT(VARCHAR(320),ITEM_CODE),
         ITEM_DESC= CONVERT(VARCHAR(320),ITEM_DESC),
         [SECOND_DESCRIPTION] = CONVERT(VARCHAR(320),   [SECOND_DESCRIPTION]), 
         [IBC] = CONVERT(VARCHAR(320), [IBC]),
         [ITEM_GROUP] = CONVERT(VARCHAR(320), [ITEM_GROUP]), 
         [Main_Item] = CONVERT(VARCHAR(320),[Main_Item]),
         AGGREGATE_CODE = CONVERT(VARCHAR(320),AGGREGATE_CODE),
         ITEM_TYPE = convert(varchar(320),ITEM_TYPE)
     FROM 
         [dbo].[RMS_Master_11]) AS t
UNPIVOT
(
  Value FOR Property IN ( ITEM_CODE,ITEM_DESC,
    [SECOND_DESCRIPTION], 
    [IBC],ITEM_GROUP, Main_Item,AGGREGATE_CODE,ITEM_TYPE
    )
) AS up;

错误消息：

  

Msg 8167，Level 16，State 1，Line 22
  列的类型＆＃34; ITEM_TYPE＆＃34;与UNPIVOT列表中指定的其他列的类型冲突。