what is at least one transport method for mandatory notifications?

[bcerk]

Greetings!

After upgrade from 4.0.6 to 5.0.4 I've noticed that if I try to modify any Agent/Operator settings via Admin menu, there comes this red message when trying to save:
Please make sure you've chosen at least one transport method for mandatory notifications.

So no change is saved, not for any agent. Only at creation of new agent OTRS allows to save, so I guess the problem comes after agent is connected with groups (roles and services are not used here).

I've searched settings for "transport", but found nothing meaningful that would not be set as default value.
Also, google seems to find nothing valueable about this.

Any idea?
Thank you in advance!

[bcerk]

For some reason I wrongly concluded that settings aren't saved in this case - but they are. So the red message is really just a warning, no problem
Though it seems it should not appear at all, because the transport method is set, and the notifications are being sent correctly.

[davidbann]

I have the same problem - while I know that it's just a warning (although it appears very much like an error and gives the impression that changes are not saved), I would like to understand what is causing this - where are the transport methods maintained?