What version of firefly are you using. That’s a fairly obscure error message – ie. not seen that before IIRC.
Suggest you download either of the the nightlies on this page:
http://nightlies.fireflymediaserver.org/
then go through the entire uninstall process via the installer prog and reinstall for one user only. You may find bugs such as the first scan hanging (run it for 5 mins or so then stop & restart) & remember to shorten the name firefly assigns the server when you set up. How goes it now?