When trying to load a server, right after it says "Logging in" the screen turns black then crashes.

I got picked to help build on a server before its released to the public. But everytime I try to load the server it crashes! The server runs on Bukkit 1.7.9 so I have to use Minecraft 1.7.9 to get on. But every time I try it crashes! what do I do? (Oh, and in the "Affects Versions" bar I cannot put in 1.7.9.)