If one does a chmod 600 /var/log/messages (essentially locking it down so that only root can read from and write to it), and then attempt to open it in the Gnome log viewer as a non-root user, the error dialog pops up:

    [error] One file or more could not be opened

    /var/log/messages is not a log file.

This is a rather silly error message, as cat on the same file gives a message that is slightly more reasonable:

cat: /var/log/messages: Permission denied

Presumably this is a "catchall" message, covering among other things the failure to open the file and formatting problems within the file.