customValidator troubles

Hi All.

What I am trying to do is use customValidator to go to a database via a stored procedure and fish out a UserName value. If it finds it, I want it to return 1 and if not I want it to return 0. On the ASP.NET page I have a field called user_username that customValidator is pointing to as a control to validate. The subroutine for the validator and my stored procedure are below. I now have 37 instances of the username = pkorolev and I get 37 as the value returned by the stored procedure, however the point where I want it to invalidate the page, the code fails. What am I missing???? I bet it is something really simple.
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create procedure userAlreadyExists
@user_username nvarchar(100),
@valid int output
as
declare @userValid int

select @userValid = Count(*) from user_pass
where user_username = @user_username


set @Valid = convert(int, @userValid) -- in this line i am simply trying to ensure that the value coming back as an iteger


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CustomValidator SUB:



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Private Sub custValUserExists_ServerValidate(ByVal source As System.Object, ByVal args As System.Web.UI.WebControls.ServerValidateEventArgs) Handles custValUserExists.ServerValidate

Dim cnn As New SqlConnection(connection.SQlConnection)

Dim sdrUserExists As SqlDataReader

Dim cmdUserExists As New SqlCommand("userAlreadyExists", cnn)

Dim ctrlValue As Integer

Try

cnn.Open()

cmdUserExists.CommandType = CommandType.StoredProcedure

cmdUserExists.Parameters.Add("@user_username", SqlDbType.NVarChar, 100).Direction = ParameterDirection.Input

cmdUserExists.Parameters("@user_username").Value = Trim(art_username.Text)

cmdUserExists.Parameters.Add("@Valid", SqlDbType.Int).Direction = ParameterDirection.Output

cmdUserExists.ExecuteNonQuery()

'the line below is for checking the value returned on the confirmation page
Session("DBRETVAL") = cmdUserExists.Parameters("@Valid").Value

If cmdUserExists.Parameters("@Valid").Value = 0 Then

args.IsValid = True

Else

args.IsValid = False

End If

Catch ex As Exception

lbltype.Text = ex.ToString

End Try

End Sub

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Many thanks

Phil