Empty itinerary (even it is not)

While process of booking some unit, in step after i filled my billing data and accepted terms, I have listed unit(s) that I choosed and button "Book it", but after clicking it I'm getting message that itinerery is empty.
If I try to book another unit, it is at that step listed together with previous one and again I get "empty itinerary" error.

Any help is appreciated.