I just recently came across this issue with a 2006 Prius that I was doing work on. I had disconnected and taken out the hybrid battery and after putting it back in and reconnecting it, the car would not go into either Reverse nor Drive. I did a bunch of googling, and couldn't find the fix. The car drove fine before I took the hybrid battery out.....
The problem was the hybrid battery disconnect wasn't properly inserted by me. This is an orange plastic piece that goes in and locks in place. Well, I thought that I knew how to do it. Turns out, you have to slide it in and lock it and then press it down to make the connection. The pressing down was the step that I was missing....
So, to help get this information out there on google for the next dummy like me, I am adding this to my blog.
Here is a youtube video about what I am speaking. Fast forward to 1:00 to see the press down portion of the operation that I skipped.