The Shared Folders section of the guest Settings window. How to share folders between VirtualBox guest and host Your email has been sent https://assets.techrepublic ...

Does anyone know offhand how to remove the guest additions for VirtualBox 3.1 in Ubuntu 9.10? These are the additions that provide mouse integration and X drivers for automatic window resizing.

It is the first thing you need to fix the issue as stated above. For that, you need to run the virtual machine showing the error and go to the Devices > Install Guest ...