I sent a Medical Examiner's certificate a few weeks ago, and now i got it back by mail, Why it was rejected?
That information can be found on the content of the letter itself.
Um, it says something about doctor not being listed on some registry?
Yes, that would be the National Registry of Certified Medical Examiners Search. If your doctor is not listed there, then you must get a new exam practiced by a doctor listed on that registry.