If you read the rating comments on CPAN you will see that several users have issues with
File::DirWalk. For all I know it might be a perfectly good module, but you might be better with the core module
File::Find, which has probably had a lot more testing.
And you certainly should not ignore error messages just because you do not understand them - error messages are your friends! Ask about them here if necessary.
And:
use strict;
use warnings;