Root of check-in does not exist

I am following the excellent article that Evan produced on using the SCM command line interface from an Ant script (http://jazz.net/library/article/195). I cannot get the Perl script running, so I am (temporarily) using the checkin command directly.

I am now seeing an error message on the checkin command...

__scm-checkin:
Problem running 'checkin':
Root of check-in does not exist: /path/to/my/foobar.jar

What am I doing wrong? Thanks,
Brian