This can be done via permissions in User Profiles:
Open the User Profiles program and select the user you wish to amend
Browse to the Authorisations tab
Click Update
In the Tasks Screen section untick the Reschedule Tasks? option
Click Save
Changes to user profiles will take effect when the user next logs into Proclaim
If you have any issues with this or do not have access to User Profiles then please raise a new case online and reference the title of this article.