I believe that the "old boys network" is still up and running. When I started out in airline flying my application to an airline sponsorship scheme became blocked - I didn't find this out until I had got my licence myself and came to apply to another airline.
All appeared to go well until there was a sudden U-turn. Luckily I happen to know a few people in airlines too, and I managed to find out what was going on. Someone I had previously worked with a few years back, her husband was a pilot, and I'd had a fairly minor falling out with the person I was working with. For some reason he had decided to launch a personal campaign to stop me getting employed. This involved slandering me by giving false information, claiming he was a former employer of mine, and basically saying plenty of things that were not true, but never in writing. Obviously the people receiving this information would then inform whoever was doing the recruitment process and, because there was a "doubt" over my skills and ability, each time the recruitment process got stopped. Luckily I found this out and managed to block the information supply to him, so he didn't know who I was applying to - and anyway, its not like he knows everyone in the business.
But for a while I was worried that, with aviation being a small world, and this guy slandering me to potential employers, I would never get a job.
If you feel someone is doing this to you then the best ploy is to quietly try and find out what is going on - ask the potential employer about your referees - I discovered this person had claimed to be mine, even though I had never mentioned his name! Use all your contacts to get the information.