cvsweb v3.0.2 - unable to see diff

[Amy]

Hi -

I installed cvsweb v3.0.2 and everything works but the get diffs
feature.  When I click on a file to get a diff, I get version
unknown-left and version unknown-right. I checked the apache logs and
there are no errors.  Here is my url of the diff:
http://hector:1978/cgi-bin/cvsweb.cgi/ism/ism_app.pkg.diff?only_with_tag=MAIN&r1=text&tr1=1.29&r2=text&tr2=1.30

Help please. I can't decode the cvsweb.cgi script.  What do I need to
get the diff feature working in cvsweb.

Thanks in advance. :)
Amy