Parallels Plesk for Windows upgrade and lots of session files

Be careful when running the Parallels Plesk update utility on Windows servers if you have a large number of files in “C:\Program Files (x86)\Parallels\Plesk\admin\sessions” as once it has finished the upgrade the utility will try and clear this directory before letting you do anything else, including the mandatory reboot. It seems that it is quite easy for there to be hundreds of thousands of files in this folder, which in turn means that this part of the upgrade process can take well over an hour even on a decent machine!