It happened to me. It may have been started initially by a network, but then persisted either because it was my MAC address that had been flagged, or because of a cookie that stayed on the machine.
Had you recently traveled? Is it possible that the time on your device did not match the local time?
I'm thinking in my case such a mismatch caused the ban, which persisted even after I went home.
At that point, clearing the cache seemed to fix the problem. You might try that.