won't go in reverse

My 99 Altima sometimes won't go in reverse. This mostly happens when shifting from drive to reverse when the car has recently been started. Any idea what the problem is?

manual or automatic tranny?

i had a similar problem with my manual, but it was due to either:

--car was cold (no oil circulating yet)
--needed to let the car roll in neutral a couple inches, then it engaged easily

It's an automatic.

Dang then i don't know anything about that... ask JustSayGo (person on this forum).