unable to log into the system???

i have a question, yesterday my linux box didn`t allowed me to log into the system. after typing my username and password, it echoed this message to the screen:

``Login [a number here]: unable to change tty `/dev/tty1` for user so and so

Unable to change tty /dev/tty1: Bad file number``

i tried under root and other user aswell, and nothing... i got the same message... i was totally afraid that i was forced to make a re-install, losing all the customization that i`ve done to the system and the few files that i`ve created... or using a start up floppy and `linux single`, but, before that i tried rebooting the system, -it was up for more that 5 days-. after the reboot, a vulcan pinch, all went well... i can log in and everything else.
the system is allright, the only thing that i`ve noticed is that the file `issue`and the `motd` where back to their default, that means that the messages that i`ve written were gone, and instead of that there were the ones that come `from the factory`.
i don`t understand, isn`t linux totally stable? i leave the computer on all day, but only use it at nights, after work, maybe is because of that? i always log off before leaving the computer away.
perhaps a daemon is working in the background and using all the free memory? i`ve never left the machine on for so many days... but i`ve reduced the daemons to the bare minimum, see:
http://discussions.virtualdr.com/For...ML/002030.html

any advice, or idea is really welcomed.