I have a 2008 G37 coup with just under 81,000 miles on it.
And yesterday I drove around to do errands and at my last stop it wouldn't go into revers so I waited for my dad to pick me up.
So when he finally got to where I was about twenty minutes I tried it again and it went in revers just fine.
And the last time I changed the trans fluid was at bought the 35,000 mile mark.

Has this happened to anybody else?

 

i would start by checking the trans fluid and see how dirty it is. something in your valve body may be sticking as a result of dirty trans fluid. worst case scenario is there some sort of planetary gear or band problem inside the trans.