As you can see in this topic, you’re not the only one having this issue:
But all we were able to establish there is that Microsoft has trouble looking up MX records on our servers. And that this issue seems to primarily affect .com.ar domains.
Besides that, I have no idea. The error message from Microsoft doesn’t point to a clear issue to me, I’m not able to reproduce this issue on my own domain with my own hotmail.com account, and I cannot find any issues with our nameservers myself.