Comment 4 for bug 974647

You appear to have unofficial packages of the X drivers installed on your system, which prevents apt from calculating an upgrade path because the packages you have installed are newer than the versions in precise, but don't use the same X ABI as precise.

This is due to the use of the ppa https://launchpad.net/~oibaf/+archive/graphics-drivers on your system.

You will either need to manually mark this ppa for use during the dist-upgrade in the update-manager config, or manually downgrade to the official Ubuntu versions of these video driver packages (xserver-xorg-video-intel, xserver-xorg-video-ati, xserver-xorg-video-radeon) and then upgrade them again after doing the dist-upgrade.