I get this error when trying to run autotest-standalone:

C:/Ruby/lib/ruby/gems/1.8/gems/autotest-standalone-4.5.2/lib/unit_diff.rb:77:in write': Invalid argument (Errno::EINVAL)

Solution, replaced putc found at lib/autotest.rb@284 to print instead.

You will find the file at the path provided by the stacktrace:

C:/Ruby/lib/ruby/gems/1.8/gems/autotest-standalone-4.5.2/lib/autotest.rb