[CentOS] Kernel errors, resulting in system crashes

Hi Guys,

After a chat with some helpful people on Freenode I've included as much
information as I can think to about this error, if you need anything else
please don't hesitate to ask.

I run a webserver (remotely administered, no graphical user interface that
i know of - certainly not one running all the time) - in the past few days
this error has started to occur, the system dies and needs manually
rebooting after each occurence:

----------------

May 21 23:08:01 testmachine kernel: Page has mapping still set. This is a
serious situation. However if you
May 21 23:08:01 testmachine kernel: are using the NVidia binary only
module please report this bug to

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The machine runs CentOS 3 and has been for ~2 Years, a technician at the
datacentre ran Memtest earlier today which returned no errors.

Hardware wise it's an intel 2.53Ghz Celeron, 1.5GB RAM

I would really appreciate any help!

Henri