Hi @Arivu_Muthaiah ,
This might be because your client console is unable to establish a connection with the application server. Make sure you have entered correct connection URL and check for your internet connectivity is good. You can also try restarting your system.
Check with the other operators who uses the same environment - If they are also unable to login, you can reach out to Adobe support. Also, If you have access to Campaign application server, check whether it is up and running.