Summary:
After the supervisors are associated to a user, upon saving the user profile, there is an error that says 'Supervisor must not have overlapping values'. This generally happens when there are more than one supervisor associated to a user at different intervals of time and when there is an overlap. For a user, there may have been a supervisor and after a period of time, this supervisor was changed to another supervisor. However the supervisor who is currently associated to the user must have the start date the same date as the end date of the previous supervisor.

More Information:
The overlap happens as the End date of the previous supervisor overlaps with the start date of the new supervisor. This implies that the start date of the new supervisor must be at least a day after the end date of the previous supervisor.