Fix error message for failing booking
Fix error message for failing booking

OmeGak/indico,OmeGak/indico,OmeGak/indico,pferreir/indico,ThiefMaster/indico,DirkHoffmann/indico,DirkHoffmann/indico,ThiefMaster/indico,mvidalgarcia/indico,mic4ael/indico,indico/indico,DirkHoffmann/indico,mvidalgarcia/indico,indico/indico,DirkHoffmann/indico,indico/indico,mvidalgarcia/indico,pferreir/indico,indico/indico,pferreir/indico,mic4ael/indico,ThiefMaster/indico,OmeGak/indico,mic4ael/indico,mic4ael/indico,pferreir/indico,ThiefMaster/indico,mvidalgarcia/indico