Ruby: invalid byte sequence in UTF-8

I'm writing a Django project that uses the LESS language. I'm using the django-css application to do this. My colleague is getting the following error, but I am not. I suspect that this might be because the encoding is wrong on the file being compiled. The weird thing is that we cloned from the same hg repo so I don't see why his files' encoding would be wrong and mine right.

TemplateSyntaxError at /qa/
Caught an exception while rendering: /home/rajoy开发者_StackOverflow社区/.gem/ruby/1.9.1/gems/less-1.2.21/lib/less/engine.rb:49:in `gsub': invalid byte sequence in UTF-8 (ArgumentError)
    from /home/rajoy/.gem/ruby/1.9.1/gems/less-1.2.21/lib/less/engine.rb:49:in `prepare'
    from /home/rajoy/.gem/ruby/1.9.1/gems/less-1.2.21/lib/less/engine.rb:30:in `parse'
    from /home/rajoy/.gem/ruby/1.9.1/gems/less-1.2.21/lib/less/engine.rb:45:in `to_css'
    from /home/rajoy/.gem/ruby/1.9.1/gems/less-1.2.21/lib/less/command.rb:58:in `parse'
    from /home/rajoy/.gem/ruby/1.9.1/gems/less-1.2.21/lib/less/command.rb:51:in `run!'
    from /home/rajoy/.gem/ruby/1.9.1/gems/less-1.2.21/bin/lessc:102:in `<top (required)>'
    from /var/lib/gems/1.9.1/bin/lessc:19:in `load'
    from /var/lib/gems/1.9.1/bin/lessc:19:in `<main>'

I have ruby 1.8.6 and gems 1.3.6.

My colleague has ruby 1.8.7 and gems 1.9.1.

What are the possible reasons for why this is happening?

---

The Ruby version. The 1.9 changed the way String encodings are handled.

http://blog.grayproductions.net/articles/ruby_19s_string