Thanks so much for the insight here. I have updated my bios on my asrock Z170 extreme6 to version 2.60 and updated the realtek drivers to version 7543 and it has fixed my hangs on shutdown, and these ACPI errors and other USB type errors from hcmon. System shuts down fine now.
This is a bit weird, as i have been running this mobo since XMAS 2015 and only in the last month have had problems shutting down. So something changed i think at the OS level. My OS is windows 7 x64 with the asrock UEFI patch. HOwever my event log is clear now, so it was one of those two things, the bios update or the realtek driver update.
Just posting an update. It was aviria antivirus that was making my machine hang on shutdown. Absolutely no problems now for months after uninstalling that software. The problems eventually came back with the bios update and driver update alone.
