If your System Administrator User has turned on the Prospect Timeline feature and Users are recieving an Error: "SObject was retrieved via SOQL without querying the required Field: Task: Type" you will need to adjust the Field-Level Security setting for the Type Field on the Task/Activities Object.
Navigate to Setup > Customize > Activities > Task Fields
Scroll down and click on the Field labeled "Type":
Click the 'Set Field-Level Security' button:
Be sure the Field is Visible to All User Profiles: