que pasa con este ERROR URGEEEEE

Saludos :

miren tengo este codigo

Dim cn As SqlConnection = New SqlConnection
(connectionString)

Dim strSQL As String = "SELECT CVEUSR, PASUSR FROM
COPUSERS WHERE CVEUSR ='" & usuario.Text & "'" & _
" AND (PASUSR = '" & password.Text & "'"

comando = New SqlCommand(strSQL, cn)
cmd = New SqlDataAdapter(comando)
dt = New DataTable()
cmd.Fill(dt)
n = dt.Rows.Count

Y ME ENVIA EL SIGUIENTE ERROR

Login failed for user '(null)'. Reason: Not associated
with a trusted SQL Server connection.
Description: An unhandled exception occurred during the
execution of the current web request. Please review the
stack trace for more information about the error and where
it originated in the code.

Exception Details: System.Data.SqlClient.SqlException:
Login failed for user '(null)'. Reason: Not associated
with a trusted SQL Server connection.

Source Error:


Line 54: ' Dim ds As DataSet = New DataSet()
Line 55: dt = New DataTable()
Line 56: cmd.Fill(dt) AQUI ES EL ERROR
Line 57: n = dt.Rows.Count
Line 58: If n > 0 Then


Gracias espero me puedas ayudar