was unable to authenticate because an authenticating authority was not reachable. Resolution: The server may be asking for ...

%1 was unable to authenticate because an authenticating authority was not reachable.
 
 Resolution:
 The server may be asking for Kerberos authentication and Communicator is not able to find the Kerberos Domain Controller in order to generate credentials and authenticate.  The network administrator will need to change the configuration on the server to utilize only NTLM authentication before Communicator can login from this location properly, or connectivity will need to be made available to an authenticating authority.