Q: What does "Immediate Mode Not Allowed" mean?
A: If you have a CHECKLIST or the activity is REPEATING or you have more than one ACTION - then the Action you are adding can't be set to "IMMEDIATE". IMMEDIATE actions are setup to go out as soon as the Activity is created in the calendar... this would be used for an AUTO RESPONDER for example. If any of the limitations above exist then you can send the activity "MANUALLY" or "AUTOMATICALLY", just not "IMMEDIATE".