Limited and multiple account scanning is not supported in this beta 1
release of Microsoft AntiSpyware. Check back for this in beta 2. However I'm
not aware of that specific error message, but of course, I'm not surprise it
is as a result of non-support of limited account scanning in beta 1.
Read this from Steve Dodson:
You have a limited user account running the application looking for spyware
on all files and folders. This includes the administrator account which
limited users may not be able to access. So we have to approach this
carefully in order to remove the spyware from all locations, but also
preserve file and folder permissions and access.
In short, we are addressing this for a future release, but it involves some
major coding and testing.