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