OleDbException ErrorCode

When a user finally confirms his order in a shopping cart application (using MS-Access as the backend), the items he has purchased are populated in a Access DB table named Orders & his personal details (like name, mail, billing address, shipping address etc.) are populated in another table named CustDetails. Both the DB tables have a column named OrderID. This column is the Primary Key in the CustDetails table & the Foreign Key in the Orders table. The Session.SessionID becomes the unique OrderID.

After confirming an order, if the user refreshes the page, the app will try to populate the same Session.SessionID in the CustDetails table but since the column OrderID is a Primary Key column in the table CustDetails, it won't accept duplicate OrderIDs. Under such circumstances, an OleDbException will be raised.

Since a DB app can throw other OleDbExceptions other than the one about which I mentioned above, I want to display custom error messages to the user. For e.g. if he refreshes the page after confirming his order, I want to display a message saying "Your order has already been placed".

To do this, I tried using the ErrorCode property of the OleDbException class but what I found is the ErrorCode changes from time to time! Had a particular ErrorCode been assigned to the error, I could have done something like this (assuming that the ErrorCode for the above error is -12345 which is constant):

Try
    'some code
Catch ex As OleDbException
    If (ex.ErrorCode = -12345) Then
        Response.Write("Your order has already been placed")
    ElseIf (ex.ErrorCode = <some other constant ErrorCode>) Then
        Response.Write("Another custom error message")
    End If
End Try

But I can't do the above since the ErrorCode changes from time to time.

So how do I display custom error messages to users under such circumstances?

Of course, I can use the Message property of the OleDbException class but that would be a rather tedious workaround.