This can happen sometimes, especially on a first time login from a new location.
Normally, when you log in, after a few seconds you should see a small box in the centre of the screen as shown below:
If this box doesn't appear, refresh your browser (click the refresh icon near the address bar or press F5 on the keyboard). EM-COP should then complete the log in. This is the only situation where you can do this. Once you have successfully logged in, refreshing the browser will log you out of EM-COP.