When you are stuck at the "preparing the stream" screen or SteamVR throws na error, quite often it's caused by SteamVR loading driver other than VRidge.
By default SteamVR loads drivers alphabetically and because "VRidge" is down the list it may be blocked by other drivers. There are couple possible solutions to this problem.
1. Uninstall other drivers/software similar to VRidge.
2. Reinstall SteamVR and then click the "Play" button in RiftCat client as shown on the screenshot below.
3. Also update your GPU driver, this may resolve the 306-308 error.
If you are still experiencing issues then you can contact firstname.lastname@example.org and they will assist you in resolving the issue.