"Could not find the main class: net.minecraft.client.main.Main. Program will exit." Is seen after launching Minecraft 14w28b

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
Describe what happened here

Steps to Reproduce:
1. I just try to launch 14w28b
2. Boop!
3. Could not find the main class: net.minecraft.client.main.Main. Program will exit.
4. Hail is sad... D: