Symptoms

Bug in Default client event k2 studio
 

Diagnoses

When configuring a default client event in k2 studio in the wizard, on Event Notification settings, if "Customize the Notification Message" is checked. The "From" Address control is still disabled forcing the user to de-select "Customize the Notification Message" in order to get tot he next step of the wizard. Effectively preventing the customisation of email notifications as the wizard cannot progress if no from address is added in customise mode.
 

Resolution

To get around this, the best thing to do would be to go into the environment fields within K2 studio and under mail server unchecking the default address.
Then closing the event itself reopen the mail event checked true and you will see the Default Email address return to designated field.

The address should be altered within here and only through workspace if necessary.