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