I had recently installed windows 10 on one of our computers at work. I was able to successfully add it to the domain, but then none of my users could login. The error message was:
We can't sign you in with this credential because your domain isn't available. Make sure your device is connected to your organization's network and try again. If you previously signed in on this device with another credential, you can sign in with that credential.
This error message contains pretty much no information about the problem. The domain is/was available, as I was able to join it. After some looking around, I found that the problem is I missed a setting in my smb.conf file on my samba server. I needed to add this line for windows 10 computers:
server max protocol = NT1
Restart samba and things worked fine.
Note, this page gives you all the required settings for samba domains. Since I have been using the same smb.conf file for years, I didn't have the line needed because it's a more recent addition.