Using DBM files in FDSE
DBM files are specialized data files that provide very fast lookups of data. This makes them very useful, but unfortunately they do not work on all versions of Perl. For this reason, FDSE only makes use of DBM functionality for a two non-core features: the secondary logging of search terms, and the persistence of custom metadata for edited records.
If you use FDSE on a platform where DBM files are not supported, then you will experience errors within these two non-core features. To avoid those errors, go to "Admin Page" => "General Settings" => "Use DBM Routines" and uncheck the setting to disable it. Then FDSE will bypass the features that depend on DBM functionality.
"Using DBM files in FDSE" https://www.xav.com/scripts/search/help/1169.html