Can't install guest additions to windows 8.1

[P a u l]

Windows 8.1 preview guest.
Windows 7 host.
The "Install guest additions" menu item doesn't seem to do anything.
Any help appreciated.

[mpack]

Autorun is disabled, browse to the virtual CD and install the GAs manually.

Note that Windows previews or any other betas and not supported guests.

Please restrict further discussion to the Win8.1 Preview Discussion thread.