It appears you're checking errstr more often than you should. Your code works just fine if you just test the results of the fetches. I'm sure that if a result came back undefined or empty you'd want to check errstr then. This sounds like doing die $! if $! which fails for the exact same reason - if you haven't just done a system operation then you don't know that $! will be false.

In preference to doing manual testing of of success/failure, it's much easier to ask DBI to throw exceptions for you: DBI->connect( 'DBI:CSV:f_dir=.', undef, undef,{ RaiseError => 1, ShowErrorStatement => 1 } ).