Boot Error - ACPI PCC Probe Failed

Apparently it is a harmless message related to a 'PCC' driver:

So it looks like you build the PCC mailbox driver which is new in 3.19-rc and that driver fails to load, because it doesn't find hardware to work with.

The message is harmless, but it also is not useful. The driver in question seems to be overly verbose to me in general.

That is what I gleaned from this conversation.

ACPI PPC probe failed. is related to a new ACPI interface PCC (Platform Communication Channel), which is defined by UEFI.

You may see this in your output of journalctl:

$ sudo journalctl
Aug 16 23:10:55 x kernel: **PCCT header not found.**
Aug 16 23:10:55 x kernel: **ACPI PCC probe failed.**

These are the returns if the code does not find the ACPI interface which only some very new devices have or if it actually fails to read/write to the interface if it is present. The code was written for upstream releases. If you read the emails in the filed bugs below you will find information that supports my statements and you can read the return messages in the code itself in the GitHub link above.

I hope this helps to clarify some things.

I [Solved] the problem by changing the motherboard settings. For my motherboard (access this at boot, not through Ubuntu) I went to Advanced > System Agent > Graphics > iPGU Multi-Monitor and set it to "enable." I left all of the other system agent graphics settings on auto. After that the boot and ACPI problems (including a shutdown hang, crashes, freezes, monitor shutdown) stopped.

Every motherboard vendor has its own settings. The problem seems to be a northbridge snafu between the onboard Intel graphics and the Nvidia card. So, it may takes several visits to your motherboard setup to find the right combination of settings that works for you. This problem was new to me under 15.04, and may be due to a change in how Ubuntu handles such graphics disputes.

(My motherboard is ASUS P8Z77-V LX LGA 1155 Intel Z77)