* One or more filesystems cannot be found and mounted: Check the contents of /etc/fstab - in making quick alterations here, typographical errors are common. You can use the e2label command to view the label of each filesystem: some distributions set these to the mount point so you can figure out what is what.

Is a filesystem full? This can show up in lots of different ways: being unable to save files, print jobs not spooling correctly (especially on Samba print/file servers), and so on. Use the df command to see available space: