Error setting U-Boot ethernet MAC

If you are getting error when trying to setup MAC address (variable ethaddr) on U-Boot:
=> setenv ethaddr 00:04:9F:00:AF:DF
Can’t overwrite “ethaddr”

Then you can follow this procedure:

1) Found the flash area where environment are saved (“RO” areas):

=> flinfo
  C1F80000        C1FA0000        C1FC0000        C1FE0000   RO   C1FE8000   RO 
  C1FF0000   RO   C1FF8000   RO 

Un-protect these areas:

=> protect off C1FE0000 C1FFFFFF
Un-Protected 4 sectors

Erase these areas:

=> erase C1FE0000 C1FFFFFF

.... done
Erased 4 sectors

Protect these areas again:

=> protect on C1FE0000 C1FFFFFF
Protected 4 sectors

Reset the board

Set ethaddr:

=> setenv ethaddr 00:04:9F:00:AF:DF