Windows 10 Password Error with Samba Share

You can also fix this on the server (Ubuntu 18.04.1 LTS) side: In /etc/samba/smb.conf, put:

ntlm auth = true

And it works like a charm.

if anyone else runs into this problem, my solution was to adjust the security policies on the Windows client.

Run > Secpol.msc

then I set Local Policies > Security Options > Network Security: LAN Manager authentication level to 'Send NTLMv2 response only. Refuse LM & NTLM'

and the client connects just like before.

The accepted answer is correct, and works for Windows 10 Professional and above. However, Windows 10 Home Premium lacks secpol.msc and its easy-to-use interface.

To fix this on Windows 10 Home Premium, navigate to the following key in the registry:

HKLM\SYSTEM\CurrentControlSet\Control\Lsa

Look for a DWORD value named LmCompatibilityLevel. If it does not exist, create it. Set the value to 5.

After making this change, I was immediately able to access the Samba server without restarting.

^{_{Source: Changing LAN Manager Authentication on Windows NT}}