The University has a number of licenses allowing people to access Colleague. Occasionally, however, all the licenses are in use at the same time. When that happens, other users will not be able to access the system, and an error message will appear. See below.
There is not much that you can do except wait. You should just keep on trying to log in until you can get in. If you happen to notice someone in your area with Colleague open, you could ask them to close Colleague if they are logged into the system and are not using the application.