Scenario:
In Web TimeSheet when adding a new supervisor you might get an error Supervisor must not have overlapping values.

Cause:
This occurs if the Start or End dates of two different supervisors have an overlapping Start or End dates. A user profile cannot have more than one active supervisors assigned with overlapping start or end dates.

Resolution:
Ensure that the start or end dates of supervisors assigned to a users profile, do not overlap with each other.