roger pack provided this console log, showing incompatibility between sequence and ruby-debug. Bad (re-)definition of StringIO in lib/sequence/file.rb.
require 'redparse'
=> true
require 'ruby-debug'
NameError: StringIO is already defined
from E:/installs/ruby191p376/lib/ruby/gems/1.9.1/gems/ruby-debug19-0.11.6/cli/ruby-debug.rb:2:in require' from E:/installs/ruby191p376/lib/ruby/gems/1.9.1/gems/ruby-debug19-0.11.6/cli/ruby-debug.rb:2:in<top (required)>'
from (irb):2:in require' from (irb):2 from E:/installs/ruby191p376/bin/irb:12:in'
roger pack provided this console log, showing incompatibility between sequence and ruby-debug. Bad (re-)definition of StringIO in lib/sequence/file.rb.