This photo was sent in by a blogger who would like any input you have on this problem. She has been working with a vet and has given the bird a full round of Baytril with no apparent change. She has since soften it a bit and taken off some of it. It seems keratin-like in consistency to her. (Click on photo for enlargement.)
I personally have never seen this problem. I have looked at my vet books and seen some somewhat similar problems in other birds. There are numerous causes for the problem by such things as dietary deficiency of vitamin A to various kinds of infections such as Hemophilus or Mycoplasma to mites.
If you have dealt with this problem, please post a comment to this blog!
Side note: This morning I am flying to Oakland to judge the roller show. Come on out to the show!!