One of our users is currently having problems when trying to login with Steam. We asked him to send us a log-file. We can see a "ServiceUnavailable" error saying "Failure when receiving data from the peer" in this logs.
This particular user played our game previusly (and thus alredy has linked Steam account).
User says he disabled both his firewall and antivirus.
Why is this error happening? How can we fix it?