It is almost certainly because you have not told pdk to include Crypt::Blowfish. This is speculation because I don't use this but if you are say using the Crypt::CBC example which specifies the 'Blowfish' cipher then you either need to add use Crypt::Blowfish to your code or add a command line argument telling pdk to include this module. The problem from pdk's point of view is that Crypt::CBC does not decide which Crypt:: module to load until runtime (default is Crypt::DES) so pdk does not know Blowfish is required as compile time. I expect adding a use Crypt::Blowfish to your code, and then recompiling as you have been doing should do the trick.