How do you map TimeStamp (SQL Server) to DateTime (.NET) datatype? I ran into the following error:

"Could not cast the value in field ts_times4_ to the Type TimestampType. Please check to make sure that the mapping is correct and that your DataProvider supports this Data Type."

My table:
CREATE TABLE [some_table] (
[field1] [int] NOT NULL ,
... other fields ...
[ts_timestamp] [timestamp] NULL ,
... other fields ...
) ON [PRIMARY]

My class:
Namespace abc

Public Class AtDivision
... other properties ...
Protected _timestamp As DateTime

' How do I map to data type 'Timestamp'?
Public Property Timestamp() As DateTime
...
End Property

End Class

I tried this in my mapping file, but, ran into the error I mentioned...
<property name="Timestamp" column= "ts_timestamp" type="Timestamp"/>

Thanks in advance!