I’ve just upgraded from Cubase 5 to 6. When I load a project with HalionOne in it, I find that there are no patches listed in the patch list, so I cant change the sounds. Also in a new project I get the same issue, in the patch selection list for HalionOne there are no patches available. Does this mean I am forced to go back through all my earlier projects and change my HalionOne instrument tracks to Halion Sonic SE, and that I can no longer use HalionOne in Cubase 6? From other posts it seems as though I should be able to please myself which I use, HalionOne or Halion Sonic SE. Halion Sonic SE may be an improvement, but I’m familiar with HalionOne and in many cases it does everthing I need. Another issue is that even though the project plays correctly at first, there are no instruments listed in the VSTi rack, even though I can see them in the inspector and the instruments are (at first) playing away with the original patch!! 
There’s some guidance here that may help…:-
Thanks for the link/suggestion but unfortunately it made no difference. My problem is with HalionOne and not Roomworks, as in the post at the link.
Cheers though and thanks for replying.
Aloha Deety,
I too am interested in this topic because I have many many songs that I use live on stage that use HAO.
I would like to know that with C6 I can at least continue using HAO.
I would then start new songs using HSE.
{‘-’}
Oops…! 
I do beg your pardon… I was a bit trigger happy there. Hope you get sorted soon… 
Please have a look at the Cubase 6 Read Me PDF about HALionOne on the C6 installation disc.
This is from the ReadMe.pdf mentioned above:
HALion ONE: This VST Instrument is no longer installed by default and has been replaced by the VST 3 instrument HALion Sonic SE. If you have Cubase 5 or Sequel still installed on your system, HALion ONE will be available in Cubase 6. If you install Cubase 6 with no prior Cubase 5 or Sequel installation available on the system, HALion ONE will be unavailable.
However, you may want to install it if you want to load Cubase or Sequel projects using it, or if you use content sets requiring this VST instrument (e.g. VST Sound Instrument Set Synthesizers).
To install HALion ONE, start the Cubase installer via the Cubase Start Center from DVD, use the “Customize” button and enable HALion ONE. Please note that even though HALion ONE and its content will be available after that, no VST presets will be installed! It is just provided to ensure project compatibility. Please change to HALion Sonic SE for creating new projects. The HALion ONE sound library has been included in HALion Sonic SE, so none of your favorite sounds are lost.
The problem is that I have a sound set named Synthesizer that uses HALion ONe and none of those presets work now… AND the funny thing is that they still sell it even tho its not compatible and HALion One has been drooped in C7 … http://www.steinberg.net/en/products/sounds_loops/vst_sound_instrument_sets/synthesizer.html
SO NOW WHAT??? That Library should have been transfered to HALion SOnic Ages ago…
Or maybe they did under HS SE Hybrid BUT that also is missing in CUBASE 7