The venue should have been completed in August last year but a catalogue of delays meant the opening was rescheduled for the FA Cup final in May 2006.
That deadline was also missed, forcing the FA to play the final in Cardiff.
Now Multiplex blames the venue's owners Wembley National Stadium Ltd for not starting work needed before it opens. The company rejected Multiplex's claims.
Once the building work has been finished, stadium owners Wembley National Stadium Ltd (WNSL) has said it will need two months to hold "test events" at the stadium for safety reasons before it can host a major event.
The statement from Multiplex said: "In order to achieve practical completion of Wembley Stadium certain works which are the responsibility of WNSL rather than Multiplex must first be completed.
"WNSL has not begun some of these works."
But WNSL chief executive Michael Cunnah said in a statement: "Wembley Stadium firmly rejects Multiplex's statement and refutes any claims that they make against us.
