parse': (): did not find expected key while parsing a block mapping at line 11 column 3 (Psych::SyntaxError)

It was a simple syntax error. I failed to put a space between user: and username. So it threw the same error for both the rake command, and script/about command.

You have invalid YAML code somewhere. I mean invalid for Psych (the new ruby YAML parser).

If you cannot (or don't want to) fix your YAML code, try to load the old YAML parser (syck), adding this at the beginning of config/environment.rb:

require 'yaml'

YAML::ENGINE.yamler = 'syck'