While it's the opposite of the micromanaging problem, being on the receiving end of the cold shoulder is no fun either.
Your boss seems to have no problem making some time for his favorites in the office, but when you try to book some time with him/her it never seems to happen. All of your one-on-ones seem to get canceled or rescheduled at the last minute, or worse -- your boss forgets you had a meeting altogether. The harsh reality is managers will make time for someone whenever they feel it is important enough to do so. So if you can't get an audience with your boss while others can, he/she obviously has a specific problem with you.
SOLUTION: If this has been a recurring problem you can forget email -- you need to manufacture some face-time with your boss. Scope out a time the boss is alone, walk in confidently and immediately stress to him/her you need to discuss something important. Say something along the lines of "I know how busy you are, but we seem to have had some trouble with scheduling recently and I really need to talk to you because I value your input and guidance. So do you have a few minutes?"