The driver for the Intel Management Engine Interface (MEI) is missing. The PCI Serial Port is not a traditional COM port but part of the Intel H67/Q67 Express chipset’s Management Engine.
Once installed, reboot, and the PCI Serial Port error will be resolved permanently.
Here is the full technical report on the for the HP Compaq 8200 Elite series running Windows 7 . 1. Executive Summary Issue: After a clean installation of Windows 7 (32-bit or 64-bit) on an HP Compaq 8200 Elite, Device Manager shows an unknown device labeled "PCI Serial Port" with a yellow exclamation mark.