#1 - Jan. 6, 2012, 10:04 p.m.
We have one known issue with the build that we'll be updating to today that we need to make sure you're aware of. Currently if you run the PTR client via Wow.exe it will give you an error "Blizzard Launcher has stopped working". To remedy this, you should be able to run the PTR client via the launcher.exe included in the PTR client.
This will happen once the patch is released later today. Once that is released, please post here if this does not work for you.