Grub gives messages about the boot sector being used by other software. What should I do?

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http://askubuntu.com – This only happens with one of my computers. It is an elderly laptop that has had a long and varied history with several operating systems, but in its retirement it is acting as a server for my home network using Ubuntu 12.04. It is a single-boot system, there are no other systems installed. Every so often, whenever there is a grub upgrade, I notice a message like this: Setting up grub-common (1.99-21ubuntu3.4) ... Installing new version of config file /etc/grub.d/00_header ... Setting up grub2-common (1.99-21ubuntu3.4) ... Setting up grub-pc-bin (1.99-21ubuntu3.4) ... Setting up grub-pc (1.99 (HowTos)