If you get an error on a VirtualBox guest similar to mine X Error of Failed Request Bad Window when running glxgears or glxinfo or any OpenGL game , there's many possible causes. You could have not properly installed VirtualBox guest additions. Uninstall the default guest additions (default to most distros) with sudo apt-get remove --purge virtualbox* from both guest and host.
Then reinstall virtualbox on the host and reinstall guest additions on the guest, making sure you download the latest version from Oracle (as of this writing 4.3.6).
If you still have problems with OpenGL on the guest, it's possible that the fglrx drivers were improperly installed. See this excellent post on how to remove and reinstall them.
I successfully installed the amd-catalyst-14.1-betav1.3-linux-x86._64.zip drivers with those instructions. Make sure to checkout the link to the wiki and use your distribution instead of Ubuntu precise (for example use Ubuntu/saucy for Linux Mint Petra).
You should be able to uninstall and purge any amd driver and reinstall with those instructions.