I'm not sure about what exactly to tell you but I'm guessing the bark may not be working for you if you mist it twice a day, if I'm understanding you correctly. It may be staying too moist, which is rotting the roots.
Have you tried semi hydro or 'spag and bag'? I can tell you what I was told to encourage the roots. This is the link for the s/h; http://www.rv-orchidworks.com/orchid...epi-bloom.html . Now I got a hint for this method from one of the senior members; put some rooting compound in the water when you pre-soak the clay balls over night, dust the rooting compound on the orchid roots as well before setting it up in the s/h. I have done this and it has worked, you can do the same prep before trying the 'spag and bag' too. Depending on your environment, humidity levels and such, you may have to reduce the level of water in the s/h container. I have very little to no water in mine, because of the condensation, it stays moist without actually sitting in the water. I've had only tried 'spag and bag' once, since sphagnum moss isn't sold here I used news print instead, so I guess it's 'paper and bag', lol.
After all that, I hope it works out.