How are you invoking the debugger? With  perl -d my_script? or /usr/bin/perl -d my_script?

On my machine(s) perl is the Perl that came with my version of Ubuntu (5.8.8, as I recall). The Perl I do most of my work on is in /usr/local/bin/perl (currently Perl 5.10.1).

All the Modules I down-load from CPAN end up the the 5.10 hierarchy, so a simple perl -d would get a Module Not Found error...