Optiplex 755 - How to disable Active Management Technology

I have two new Optiplex 755 Tower PC's running Dell BIOS A09.

After a clean XP1 installation I get a device error for a PCI Serial port which went away after loading the Dell drivers for Intel Active Management Technology (AMT). The device manage now shows the PCI Serial port as being Intel(R) Active Management Technology - SOL (COM3).

My problem is that these PC's are not going to ever be connected to a corporate network and therefore cannot take advantage of the AMT. This means that the event log constantly reports an Application Error in the EventLog as:

Event ID 2002

[UNS] Failed to subscribe to local Intel(R) AMT.

To get rid of the error I first tried uninstalling the AMT drivers but this put me back in the original situation with the PCI Serial port error in the Device Manager. So I reinstalled the drivers then disabled the three AMT services and also deleted the following registry key:

 HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run "atchk"

(I found information on disabling the services and deleting the registry key in other similar forum discussions)

Can anybody tell me if what I have done is incorrect or is there a better way to disable AMT.

Thanks