PT11HD can't relaunch/select new playback engine

Win8 x64, PT11HD, HD Native card.



Have PT10HD running on the same system.



After installing PT11HD, can't get it to start,

keep getting same message after every restart :



Pro Tools will now quit. Relaunch it to use the new

playback engine.



Can't get to playback engine selection.

PT10HD still running fine..



any ideas ?



thx