I didnt get back to the original post before it closed so for the sake
of anyone else arriving here with the same problem.
The problem is that the .co.uk WHOIS response includes some --- chars
that confuse the Ruby YAML parser.
Essentially, this is a Syck (the Ruby YAML library) bug.
Syck is no longer maintained and it's going to be replaced with Psyck,
the library created by Aaron Patterson.
In Ruby 1.9.2 you can already switch to Psyck.