should be the reason for rejection. First ask them if they have a QUOTA for your nationality+position+gender. If they do, the problem is with yourself.
Have you ever worked in qatar? Have you ever had a residency here? If NOT, what also could be is that your name is similar to someone's name who is blacklisted in Qatar. If this is the case, you have to prove somehow that you have never been to Qatar, and had no any negative records here.
Good luck.