Autotest error on XP

I'm having an error running autotest on XP.  I'm following Peepcode's TDD tutorial and I came across an error where I didn't have a diff.exe.  So I installed it, added it to my system environment variables and now when running autotest, I get the following error:

c:\ruby\bin\ruby -I.;lib;test test/unit/journal_test.rb -n "/^(test_should_creat
record)$/" | unit_diff -u; c:\ruby\bin\ruby -I.;lib;test test/functional/journal
controller_test.rb -n "/^(test_should_create_journal|test_should_update_journal)
" | unit_diff -u
c:/ruby/bin/unit_diff:18: invalid name for global variable - -u; (NameError)

Anyone know about this invalid name for global variable error that I'm getting?  Thanks for the help.