Same problem here as well after uptime of 4 weeks....ROS 6.12 RB2011. no buffer space available... Network doesn't work. After reboot everything ok. I tried to update the firmware but does not help.
You mean you cannot access it anymore ?I cannot access the switch with your backup.
Perhaps access to RB250GS could be more helpful, please write to firstname.lastname@example.org and open a ticket about this problem.