WebRTC createOffer error <unavailable>

Question

Using Firefox 53.0.2 (32bit) on Windows 10 64 bit.

I am getting error when trying to createOffer on a RTCPeerConnection in which I have not added any local media stream and set

var sdpOptions = { 'mandatory': { 'OfferToReceiveAudio': true, 'OfferToReceiveVideo': true } }

I can´t get more information about it, any ideas on what might be happening or how to get more information?

Best regards,