Looks like your Test::Harness is broken. Although this is a core module, it is being actively enhanced and maintained, so I would try getting and installing the latest version off CPAN. But you might be getting more serious problems with other core modules and the 5.6.0 build.
Another possibility is a problem with something in your @INC path - directories, permissions and the like. Can you see a Test/Harness/Straps.pm anywhere there?
perl 5.6.0 is quite old now; it's also quite buggy from what I remember. Release 5.6.1 fixed most of the bugs, and is quite stable. There are further point releases in the 5.6 scheme, but don't contain anything major after 5.6.1.
If you are looking to build a new perl, I recommend going to the latest 5.8.x release, which is 5.8.6 - November 2004.