Guest account profile won't load

I decided to set up a guest account on my laptop. I enabled the guest account but when I tried to log in to it I got the comments "The User Profile Service service failed the sign-in. User profile cannot be loaded." [I haven't mistyped that, by the way, the word "service" does appear twice, believe it or not.]

I looked in the registry editor (rather nervously as I'm a bit out of my depth there!) but there is no guest account in the profile list.

Does anyone have any idea what could be the problem? Thanks in advance for any advice.