How do I fix "Authentication failed because NTLM authentication has been disabled"?

This error means Windows tried to authenticate with NTLM and was blocked from doing so — usually by how you connected, or by a security policy that restricts NTLM.

Why NTLM gets used (and blocked)

NTLM is the older challenge-response authentication family. It's still supported for workgroup and local accounts, but Microsoft's direction is to prefer Kerberos and reduce NTLM use, and hardened environments restrict it. Two things commonly force the NTLM path and then trip this error:

• Connecting by IP address. Microsoft explicitly recommends not connecting to shares using IP addresses — an IP connection can't use Kerberos and falls back to NTLM.
• An NTLM-restriction policy on the PC (Network security: Restrict NTLM) blocking the fallback.

The fix

1. Connect by hostname, not IP — use \\DiskStation (the NAS name), not \\192.168.x.x. This is the single most effective step.
2. Ensure the PC and NAS are in the same workgroup and that you're using a valid NAS username and password.
3. If a Restrict-NTLM policy is set, review it with your administrator rather than blanket-disabling security.

What not to do

Don't weaken authentication policy as a blanket fix. Prefer Kerberos (which works when you connect by name in a properly configured environment), keep credentials valid, and avoid IP-based connections. If the data behind the share matters, make sure it's backed up regardless of the connection issue.