Problem running sql query on sql express

I am running a query on a few servers, it works fine on all SQL 2008 R2 and up. But when I ran it on an SQL Express 2005 I got an error.

This is the query:

SELECT ExpiresOn as originalValue,
    CONVERT(VARCHAR(25), CONVERT(DATE, ExpiresOn), 101) as newValue
    FROM Users
    WHERE ISDATE(ExpiresOn) = 1

This is the error:

Type DATE is not a defined system type

Is there a way to tweak the sql above so it works on 2005 ?   Meantime Ill advice my client to update their SQL.