I have 2 1841 routers that match IOS versions and their config match. I can get the config for the local modem but the remote modem attached to it gets the Failed to fetch config using TFTP. Running the credential check on each one passes the telnet and ssh test and fails the tftp test. Why do both fail the TFTP test but the one still is able to fetch the config. What causes TFTP test to fail?