Rails 3 YAML parse error and RedCloth

I moved a Rails 3.0.5 application to a new server with ruby 1.9.2, under rbenv. It had been working fine before but now I got this:

$ rails server
/Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/psych.rb:148:in `parse': couldn't parse YAML at line 183 column 9 (Psych::SyntaxError)
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/psych.rb:148:in `parse_stream'
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/psych.rb:119:in `parse'
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/psych.rb:106:in `load'
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/RedCloth-4.2.2/lib/redcloth/formatters/latex.rb:6:in `<module:LATEX>'
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/RedCloth-4.2.2/lib/redcloth/formatters/latex.rb:3:in `<top (required)>'
[...]


There are a lot of posts about this error on the web. Some recommend specifying the 'syck' Yaml engine in the boot.rb file or messing with your libyaml setup. This did not work for me.

The solution turned out to be simple. You can see from the error message that the error is coming from the RedCloth gem. Previously I had been using version 4.2.2 (look in Gemfile.lock) even though I had not explicitly set that version.

On the new system I had version 4.2.9 installed. When I set this explicitly in the Gemfile I could start up the server just fine, after running 'bundle install'.

gem 'RedCloth', '>= 4.2.9'