Symptoms

(more)button is disabled and the From is not able to be populated and this means we can’t move to the next screen.

Diagnoses

Check the from address value and make sure "Mail server" is default
 

Resolution 

1. Open K2 Studio.
2. Go to Object Browser -> Mail Server.
3. Check If “From Address” is (default)
4. Change the Default to “Mail Server” by right click on “Mail Server” click set as default.

Now open a process -> user action -> in notifications the from address appears.