Liffty

[Triathlete]

Soak the bolts with penetrating oil to help loosen up any rust and built up gunk! Put a bunch on and repeat a few times until your next battle with the wrench. Also tap the bolt head with a hammer. This will help loosen things up also. If all else fails a little heat from a tourch may help (just be aware of your surroundings...wiring, fuel lines, etc.).
Also, I have no idea what kind of tools your using but, in the long run one good tool is cheaper than 2+ cheap tools.

[Ldub]

...What Triathlete says, & make sure to get the threads on the top side of the adjuster as well, if that doesn't work...air impact, make a reference mark on the socket & turn the nut with short bursts.

[ZEUS]

It would probably help to take a wire brush to those threads as well - and like I mentioned, a slide bar with a socket works really well.