Error When Sending Mass Mail from a Short List

When sending a Mass Mail from a Short List a user may see the following error: 

A common cause of this error is when the Jobscience Recruiting package has been upgraded to 4.9xx without Activity Tracking being enabled on the Engagement Program object.

1. Go to Setup > Object Manager > Engagement Program.
2. Click the Edit button.
3. In the Optional Features section ensure there is a checkmark next to Allow Activities.
4. Click Save.

The full Jobscience 4.9xx Upgrade Run List with all Post Deployment Steps can be found here.