Cannot shift out of park!!!!

My friend has a '95 Sentra and when he puts in park gear shift locks. He can't even push the button in. After rocking the car back a forth a few times it allows him to shift gears. What could the problem be?

i use to have an accord automatic and when it did that it was one of the small fuses that was burned out, but i havent done it for a sentra. my advice check all the fuses to see if any are burned.