VirtualBox - shared clipboard not working

Months ago I followed these steps and got shared clipboard working: https://superuser.com/a/42140

Now, I didn't shut off my VM for several days, but instead just saved the current state. I powered it off then turned it on, and now the shared clipboard is not working.

I'm running CentOS 6.5 if that's any help.

If you have updated your CentOS kernel you would most likely need to reinstall VBox Guest Additions. While doing that I would also update VirtualBox to the latest version and grab the latest Guest Additions ISO. Then mount the ISO in CentOS and run the installer as root. After all that you can enable your Shared Clipboard.