Question : Arithmetic overflow error converting expression to data type datetime

I have a SQL Serve table with a date filed that has data that is not similiar.


CREATE TABLE [dbo].[tbl_research_mktcap_index](
      [autoid] [int] IDENTITY(1,1) NOT NULL,
      [_date] [nvarchar](50) NULL,
      [allshareindex] [nvarchar](50) NULL,
      [marketcap] [nvarchar](50) NULL,
      [deals] [nvarchar](50) NULL,
      [volume] [nvarchar](50) NULL,
      [_value] [nvarchar](50) NULL,

The _date filed is not a real data field but the data in this database is a date. The dates come in the following format

07-May-03 also 07/05/2003 and also 07-05-03

The problem is , the database was originally an access database and so I could use the following SQL statement

strSQL = "SELECT DISTINCT YEAR([_date]) As Year FROM tbl_research_mktcap_index ORDER BY 1"

 and it worked, but now with MSSQL, I get the following error message

[Microsoft][ODBC SQL Server Driver][SQL Server]Arithmetic overflow error converting expression to data type datetime

How do I make MSSQL see the _date cells as date data?

HELP PLEASE!

Answer : Arithmetic overflow error converting expression to data type datetime

something like
strSQL = "SELECT DISTINCT YEAR(CAST([_date] AS datetime)) As Year FROM tbl_research_mktcap_index where (not (_date is null)) or (_date='') ORDER BY 1"