As far as I know most of the TechNet Virtual labs are using Windows 2008 Server Beta 3 (Labs Link) for mosts labs and the systems that they run these labs on is Virtual Server 2005.
Depending on which lab you are running and the scenario that lab involves there could be any number of reasons for the error you are seeing. Parts of the Lab maybe locked down with Group Policy restrictions or may have none. You may have found a bug in the 2008 Server Beta 3 build which is quite old now and many fixes are in the latest builds of 2008 Server.
At the end of any TechNet Lab there is typically a survey supplied to you to give the team feedback about the lab. I would suggest that you fill out that feedback form and in the notes section of the feedback survey add in the issues that you found whilst using that lab.
There is not much we can do here on this forum regarding TechNet Virtual Labs and you are best to contact them directly through either the Lab Survey or if you have no luck use the TechNet Contact Us page.
Cheers,
Stephen Edgar