i seem to forget how to do this every time i need to actually do it…

if you have an expired cert on a windows terminal server then restarting the “Terminal Services Configuration” service should auto-generate a new cert. opening up a remote Certificates MMC should allow you to export the newly generated Remote Desktop certificate. these auto-generated certs seem to only be good for six months at a time.

source:
http://social.technet.microsoft.com/Forums/en-US/winserverTS/thread/1b528a7b-882a-4dc0-bb63-e36968cc284d/