We have recently rolled out an important code change that may be causing 401s in server to server requests to the REST API. Server to server requests to http://api.msappspace.com will result in a 401 now. The domain must be http://api.myspace.com. The former domain is to be used for user-agent to api requests and the latter is only for server to server OAuth signed requests.
Our own API tool has not been changed to reflect this, but will be soon.
We apologize for the invconvenience, but this was a necessary security change.