Well, I did RTFM of both modules, but missed some parts apparently.. Like $DB_HASH instead of DB_HASH. I'll blame DB_File API for mixing up C-style constants and Perl-style constants. I can also blame myself for not copy&paste the code like I did for the BerkeleyDB example. It seems that it was the -Property => DB_DUP | DB_DUPSORT that prevent the code to run. When I comment this option, the script works. Well, thanks anyway.