Just a thought:

You may need to replace this:

tie (my %hash, 'DB_File', $file, O_RDWR, 0600) || next;
[download]

with this:

tie (my %hash, 'DB_File', $file, O_RDWR, 0600, $DB_HASH) || next;
[download]

See DB_HASH of DB_File.

Update: The code shown is a fragment which does not compile. Please post a complete example if possible; or, at the least, indicate which line in the fragment shown is the line 66 referenced in the error message.

Plus minor edits.

HTH,