Hi,
This issue has been reported, and resolved, in the latest release of CPANPLUS.
As mentioned in the ChangeLog:
* address: 26077: dependency on itself; CPANPLUS had a
depenendency on the shell class you set as a default, even
if that was a shell provided with CPANPLUS itself.
This caused CPAN.pm to throw a fatal error, as it did not
know how to resolve this dependency. CPANPLUS users were
unaffected. Now, no dependency is added if the selected
shell is bundled with CPANPLUS itself.
Kind regards,
Jos