You try mapping a drive using either the guest account or an user account with no password and you get this message:

You can’t access this shared folder because your organization’s security policies block unauthenticated guest access. These policies help protect your PC from unsafe or malicious devices on the network.

Mind you, it is not smart to use the guest account or an account with no password. however I know there are situations where that is the only solution for the application.

To resolve this – on the client machine –  start regedit

Find
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters

Find the Dword

AllowInsecureGuestAuth

Set the value to 1

Close the registry editor.

Reference: https://docs.microsoft.com/en-us/troubleshoot/windows-server/networking/guest-access-in-smb2-is-disabled-by-default