This usually happens when the app cannot connect to the online service.
Please check your firewall, and make sure that CatLight.exe and LocalWeb.exe processes are allowed to connect to the Internet.
If you use a proxy server that requires manual configuration, you can go to Edit menu/Settings/Proxy and provide connection details.
For more information, you can check the application logs at %AppData%\CatLight\Logs\log.txt
Here is a sample error message, indicating a connection problem:
Cannot create account System.Net.Http.HttpRequestException: Error while copying content to a stream.