virtualbox.org

I updated VirtualBox from 3.0.4 to 3.0.6 and my virtual Win7 x64 machine won't run (Win XP SP3 host).
I had to downgrade to 3.0.4 and everything is working perfectly

Any ideas?

Please check the Discussion topic of the 3.0.6 release. There you will find the answer as of why. You should have searched, as we state in the Forum Posting Guide. I'm locking this topic because it's discussed in several topics.