Appliies Fedora/Redhat/CentOS,etc., but I have just using the OSes mentioned:

I started to run into this with ext3 when changing mount points:
From the /etc/fstab

LABEL=/backup /backup ext3 defaults 1 2

mount /backup

Error message:
mount: special device LABEL=/backup does not exist

tune2fs -L /backup /dev/cciss/c0d2p1
tune2fs 1.39 (29-May-2006)
mount /backup