Boeing scrambled on Monday to iron out contract problems that forced it to postpone the inaugural delivery of the latest version of its 747 jumbo jet, driving down its shares.

The U.S. planemaker was due to deliver a freighter version of its significantly revamped 747-8, a stretched version of the legendary 747, to Luxembourg-based Cargolux on Monday.

But in an embarrassing setback, it was forced to scratch a lavish three-day celebration, including a surprise musical act, after receiving a letter from the European carrier on Friday.

Boeing shares were down 2.3 percent at $63.89 on the New York Stock Exchange in mid-session.

Both sides blamed contract issues for the delay, a key disclosure after the program was beset by technical problems that pushed it back around two years. A performance problem could have cast greater doubt over subsequent deliveries.

We had a party planned for today, Randy Tinseth, vice-president of marketing at Boeing Commercial Airplanes, told a conference in Barcelona.

We have some contract issues which need to be resolved and we are working on that, he told the ISTAT aircraft finance conference.

Cargolux, which has ordered 13 of the jets worth $319 million each at today's list prices, threatened to look for other aircraft if the dispute could not be resolved.

In the event that the issues cannot be resolved in a timely manner, Cargolux will source alternative capacity to fully meet customer demand and expectations ahead of the traditional high season, it said in a statement.

The party-pooping postponement came a day after the head of Qatar Airways took a board seat at Cargolux following the Gulf airline's decision to take a stake of more than a third in the Luxembourg-based freight carrier.

Aircraft analyst Scott Hamilton said the Cargolux delivery had become embroiled in a wider dispute between Qatar Airways and Boeing over late-delivery penalties for the 787 Dreamliner, its latest carbon-composite passenger jet.

Qatar Airways Chief Executive Akbar Al-Baker regards the penalty for delayed 747-8 deliveries as a benchmark for other future penalties, including the future 787 Dreamliner, he said.

Boeing plans another lavish ceremony for the first delivery of the revolutionary lightweight 787 passenger plane to Japanese customer All Nippon Airways <9202.T> between September 26-28.

The Cargolux delivery was due to be followed by other deliveries to airlines or freight carriers, culminating in a 467-seat passenger version later in the year.

Boeing plans to deliver a combined total of 25-30 of its 747-8 and 787 aircraft this year, the majority being 747-8s.

Boeing's Tinseth, meanwhile, said the company expected to receive hundreds of fresh orders and commitments in coming months for its recently revamped 737 MAX narrowbody jet.

The planemaker has 496 commitments for the aircraft, which it hopes will rival a re-engined Airbus, the A320neo, which has notched up more than 1,000 orders and commitments.

(Additional reporting by Ben Deighton, Kyle Peterson; Editing by David Hulmes)