I have had similar issues, what are you getting on the receiving end? A debugging console, such as the one built in to Chrome, should give you the payload coming back from the server. One trick I have had to do is set the root key manually,
0.9.1 had some regressions so they re-released 0.9.0 as 0.9.2. The fix for Rails 4.2 is in 0.9.1 and in the 0.8.x branch, but not in 0.9.2. So I locked to 0.9.1 for now. What a hot mess!