Write more details, what exact version of VirtualBox, the kernel version in the guest and on host, edition server/desktop architecture?
Recently put on one computer VirtualBox 4 (GUI) + Ubuntu 10.10 Desktop amd64 and VirtualBox (Headless) 3.6 + Ubuntu 10.10 Server amd64. Everything was fine, except for the two cursors in the window. On a server without x rabatel via VRDP. After ustanvoki Guest Additions OK now. What is the amount of RAM allocated to the guest? I had a problem with the Unity installer, it is in the config file more than 4 gigs flew with the installation.