I have bought a new Samyang 14mm f2.8 ED AS IF UMC lens for my Nikon D7000 dslr. I was trying to set the interval timer shooting to take a time-lapse but I couldn't see the option enabled. The date and time settings are enabled and I am using a SanDisk extreme 16gb memory card. I switched to my Nikon 70-300 lens and the interval timer shooting option got enabled. Please let me know if I am missing something or if the option doesn't get enabled for manual lenses.
My guess is, Turn your Self Timer off.
Or Remote is another possibility, turn that off.
Try the standard Single Frame choice.
I know you mentioned the 70-300 lens, but a manual lens is not a factor on my Nikon.