DRM errors on startup
There is an entry for this bug on a Kernel Bug Tracker: bugzilla.kernel.org/show_bug.cgi?id=79261 It seems that this error message should be a debug message only, so nothing serious. It has been fixed anyway in 4.3.0-040300-generic
In my experience, i have accidentally caused this by installing ubuntu with UEFI "Secure Boot" enabled, and then trying to boot with "Secure Boot" disabled, try re-enabling it in your BIOS if you have it disabled.