Last week's RBTools release brought a lot of great improvements to Perforce, but it also brought an obnoxious bug along for the ride. To post a review request or run any of the other RBTools commands, you had to be in the root of your Perforce checkout.
RBTools 0.5.7 corrects this bug. If you're a Perforce user, you'll want this release. Otherwise, upgrade if you like shiny new version numbers, but you won't see any differences.
See the release notes for the same information.