I'd recommend NOT doing fsck from BackupMenu. More often than not its attempts to fix errors will lead to more problems. Instead, I'd recommend booting to BackupMenu and selecting mass storage mode (the "w" key). That will export all partitions via USB, including rootfs and optfs. Then you can fsck them from a desktop Linux PC with a more up-to-date fsck. Even better, dd the entire partition to the PC, fsck it offline, and if and only if it turns out OK, dd it back.