The door will not open; the lock must be out of order.
Not sure this sentence makes sense, or may be incorrect gramatically. I think “se abre” in present tense should be used here. And the translation is funny… I think it should be: La puerta no se abre; el cerrojo debe estar roto//The door won’t open; the lock must be broken
I agree, Spanish doesn’t use the future like that, it should be abre. I think it’s just a literal translation.
There’s a second error in that it should be ‘el cerrojo debe de estar roto’, because ‘deber + inf’ = obligation, while ‘deber de + inf’ = supposition/guess, which is what must means here. (This is a bit of a nitpick because even native speakers confuse these.)