The latest version of Virtual Mix Rack (VMR 188.8.131.52) is available in 64bit AAX format only, so it is incompatible with Pro Tools 10.
If you have updated VMR and lost visibility in Pro Tools, you can uninstall VMR before installing the previous version (184.108.40.206). Please use the uninstall command found in Applications/Slate Digital/Virtual Mix Rack. You will be asked to enter your system password. Text will not display when doing so.
Once that's done, use a link below to install the previous version: