Hey meydrew,
For problem #1, are you sending your api key along with the request (either in the header named X-API-KEY or in the URL like api_key=12341)?
For problem #2, we haven't changed the next.xml api call. We have made some upgrades to how we handle that request, so there might be regressions we weren't aware of. Can you send me the URL you use to request the next mix (including whatever headers and query arguments you use)? You can use a place holder for your API key since I don't need to know what it is.
Cheers,
Peter