Error 'Insufficient Privileges' when you try to delete records

 There are three scenarios in which a User can delete a record:

1. The User trying to delete the record is the owner
2. The User is higher than the owner in the owner's role hierarchy.
3. The User trying to delete the record has the 'Modify All' permission.

If none of the above conditions are met, the user will receive an "Insufficient Privileges" error.

Users below you in the role hierarchy may have read/write privileges via sharing model rules. However, they may not delete records owned by individuals above them in the hierarchy.