You need to verify that you have valid values for both of your request variables that are used in your update -
Do a response.write of the update statement to see if it is valid. I notice that you are using both the form and the querystring to get values - which perhaps is okay, but not commonly done and might be the cause of your problem.
Comment out the "Conn.Execute" line and replace it with the following two lines. This will display your sql so you can verify it is correct:
response.write "Update Tabela set Username='"&request.form("user")&"' where id="&request.querystring("edit")