It may happen because you have an outdated packaged.details or modlist.data file. I'd try the following:
- Make sure you've shut down the CPAN shell.
- Delete the mentioned files from your cpan directory (rm ~/.cpan/sources/modules/0[23]* usually does the trick; adjust if you use a different cpan directory)
- Try again.
If that doesn't work, force CPAN to use a mirror which you know is up to date.