There's no need for Guest Additions to copy text between host and guest machines in VirtualBox. To enable copying and pasting ...

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 ...

If the “Auto-resize Guest Display” is greyed out for you, go ahead and reboot your virtual machine and check if the issue is resolved. In case that doesn’t work, go ahead and restart your VirtualBox.