Start button —>Run —> regedit —> enter
Then go to:
Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters
Open folder «Parameters» and there you’ll find «AllowInsecureGuestAuth». Double click on «AllowInsecureGuestAuth» and change «Value Data» to 1 instead of 0. Clik OK and that should be all.