Autounattend.xml and unable to complete install

Hy folks

I've a problem (small??) during my unattended setup on vista. All
works fine and I'm able to reach the end of the installation, while
just after (or immediately before - I'm unable to determine this) of
the call of

<RunSynchronousCommand wcm:action="add">
<Order>100</Order>
<Description>Fine installazione</Description>
<Path>%WINDIR%\system32\sysprep\sysprep.exe /
quiet /oobe /reboot</Path>
</RunSynchronousCommand>

I got an error message that Windows cannot complete the install. For a
while I can see the desktop and vista seems to run perfectly but after
that the system log off and restart, and on next reboot, I get another
message, always about some error, and the loop start again (log off
and reboot).

I'm not able to figure out the matter. I don't see how look for a
possible cause: the message is outstanding for me and I don't know if
a log exists.

I'm testing my iso on Virtual PC 2007. Could be this the problem?

I read about a CTRL+Shift+f3 key combination during OOBE operation,
but in my case I don't get results. Can someone explaing me what this
command needs? And also what exactly does the Synchro Command above?

Thanks
Andrea.