New MIME type enforced in latest builds

The official W3C says that the MIME type for VoiceXML is "application/voicexml+xml," while Prophecy has been using "application/xml+vxml."

In the latest builds, that doesn't work; although Voxeo will likely add backword compatibity for the next official release, you might as well get ready now and migrate to the official type if you build supports it.

The symptom, by the way, is that dialogstart fails with a error.dialog.notstarted.