This could mean that the Server application is not running. Perhaps you've made some changes in the Server Settings or have just installed it for the first time. Go to the Server application and click OK in the bottom right hand side of the Server window. Wait until the Server states 'Server Ready' and then log in through the client application (the server always needs to be running in the background). Check if your colleagues can login, is that the case? Then proceed to step 2!It could also mean that you / your computer changed network and you're no longer in the same network as the server and thus the connection to the server can't be established. Please check if your colleagues can login. If they can login ask/check what network they are using.