There are not currently any low-cost airline routes between Pantelleria and Rome (Fiumicino) with Blu-express.
Instead you could try browsing budget flights between Pantelleria and Rome (Fiumicino) with all airlines.
Another option would be to try browsing all low-cost airline routes to Rome (Fiumicino) or all budget routes from Pantelleria.
In the meantime, this error has been logged.