Pareil de mon côté et j'ai résolu le problème grâce à cette solution:
Credit goes to Gui CrocBane for finding this solution, I'm only writing it down here step by step to help out others.
For me, the error seemed to be caused by the language region independence, introduced in the Xbox One summer update. While you can now chose a language independently from your region, Ryse still acts old fashioned in this regard.
Basically, what you want to do is set your region to your actual location (Xbox One settings>System>Language and Region) and, change the language to match your region.
For example, I am from Belgium, I play my games in English and I am currently based in France. All I had to do was changing my region to France and the language to French. I rebooted my Xbox and started a multiplayer game of Ryse. I was finally able to earn in game gold.
For other people setting your Xbox region to the UK and the language to English also seemed to have worked (not for me unfortunately).
Side note: all the gold that you should have earned in the past while you got the error is now lost forever, so unfortunately this fix doesn't work retroactively.
I hope this helps! Good luck!
https://www.trueachievements.com/forum/viewthread.aspx?tid=843373