How do I resolve this error when installing the Forge source? [closed]

The problem is that Mojang changed the download locations for their files, and with the whole Forge team preparing for the 1.7.X version launch, they aren't able or willing to touch the "stable" 1.6.4 one.

The fix involves editing your fml/fml.py file (located in the same folder as the install.cmd or install.sh file you're using to set it up).

In line 1149, change

default_url = 'http://s3.amazonaws.com/Minecraft.Download/libraries'

to

default_url = 'https://libraries.minecraft.net'

In line 1242, change

base_url = 'http://s3.amazonaws.com/Minecraft.Resources'

to

base_url = 'http://resources.download.minecraft.net'

Source: http://www.minecraftforge.net/forum/index.php/topic,14567.0.html