Grub does not autoboot the default option after upgrade to 12.10

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http://askubuntu.com – I recently upgraded Ubuntu from 12.04 to 12.10 and since that time, the system does not automatically boot. It always opens the boot menu, and I have to press Enter to make it boot Ubuntu. It seems to be ignoring the timeout value, and using a 'neverending' timeout. There are no other systems (no dual boot), only the options originally installed by default Ubuntu 12.04 installation. My /etc/default/grub has only these effective options: GRUB_DEFAULT='Ubuntu' GRUB_HIDDEN_TIMEOUT=1 GRUB_HIDDEN_TIMEOUT_QUIET=true GRUB_TIMEOUT=1 GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debia (HowTos)