You are attempting to map a drive from a Windows 10 machine to a share on a Samba server and you get the message:

You can’t access this shared folder because your organization’s security policies block unauthenticated guest access

Cause:

This change in default behavior is by design and is recommended by Microsoft for security.

A malicious computer that impersonates a legitimate file server could allow users to connect as guests without their knowledge. Microsoft recommends that you do not change this default setting. If a remote device is configured to use guest credentials, an administrator should disable guest access to that remote device and configure correct authentication and authorization.

Windows and Windows Server have not enabled guest access or allowed remote users to connect as guest or anonymous users since Windows 2000. Only third-party remote devices might require guest access by default. Microsoft-provided operating systems do not.

Fix:

If you want to enable insecure guest access, you can configure the following Group Policy settings:

Computer configuration\administrative templates\network\Lanman Workstation
“Enable insecure guest logons”

Note By enabling insecure guest logons, this setting reduces the security of Windows clients.

Reference:

https://support.microsoft.com/en-us/help/4046019/guest-access-in-smb2-disabled-by-default-in-windows-10-and-windows-ser