When you try to change "External Clock Source" in: NE Explorer--Configuration---Clock---Physical clock---Phase-Locked Source Output by Externar Clock, from 2Mbit/s to 2 Mhz you received a error message telling: "Path is already occupied, error code: 39747", and is not possible to change.
Error message: "Path is already occupied, error code: 39747", and is not possible to change":
First go to: Configuration---Communication---DCC Management and Disable "External Clock Source 1":
Then you will able to change External clock source to 2Mhz.
Note: If "External Clock Source" does not exist in DCC menu first is necessary to create it (and then set in disable):
By default, external clock source is configured in 2Mbit/s so for change it, first is necessary to disable the "External Clock Source 1" in order to not use management bits D1, D2 and D3 and system allows to change to 2 Mhz.