Do you happen to have a VPN? I had this issue exactly the same as yours, and after several other attempts to resolve (restart computer, uninstall reinstall program, etc.) failed to fix the problem I disabled my VPN and immediately was able to input the same username I was attempting before and did so successfully.
Disregard if you don't have a VPN, but if you do then it might be worth a shot to disable it and try again.
EnDarhky
Do you happen to have a VPN? I had this issue exactly the same as yours, and after several other attempts to resolve (restart computer, uninstall reinstall program, etc.) failed to fix the problem I disabled my VPN and immediately was able to input the same username I was attempting before and did so successfully.
Disregard if you don't have a VPN, but if you do then it might be worth a shot to disable it and try again.