RESOLUTION #1:
Make sure the 'Toad Web Portal (Toad Intelligence Central)' or 'Toad Web Server (Toad Intelligence Central)' service is running for TIC. These two services do the same thing, but are just named differently, depending on what version of TIC is installed.
RESOLUTION #2:
If trying to use Web Interface on the server that TIC is installed on, instead of typing the server name in the address bar, just use localhost instead.
http:localhost
If you are not including the port number in the address bar, try doing that.
http://server1:8066
If you are including the port number in the address bar and using the default port #, try not using the port number and just put the server name or localhost.
http://server1
http://localhost
RESOLUTION #3:
If accessing TIC remotely, from a machine that the TIC server is not installed on, make sure that the TIC port numbers are all open for the machine being used. Make sure there are no firewalls that are preventing them from being used. By default, these ports are 8066, 3566, and 80.