The two old pals became friends again after years of legal battles over the Doors name and Krieger and Manzarek's comeback as Riders on the Storm, and started making plans to honour their late keyboard player shortly after he died a year ago (20May13).
But the tribute gig plans have proved challenging, according to guitarist Krieger.
He tells Billboard.com, "We have talked about it and we are truly trying to get something together to do a tribute to Ray. It's just very difficult to get the kind of people that we want all together at the same time. That's a big problem.
"A lot of people said they would love to do it; we just need to get the timing right. We don't want it to be half-a**ed. We want it to be really cool. But we're working on it, and it should happen. All possibilities are open."
The film is almost half an hour longer than 'The Force Awakens'.
The film is expected to continue without Mendes' involvement.