Your first thought is probably: Who the heck still uses NetBIOS over IP? I know that Windows doesn't need it anymore.
And, you're right. Windows (at least Vista and later) work just fine without NetBIOS over IP. However, there are a lot of devices with older SMB implementations that do require NetBIOS over IP. I ran into one Sharp MFP device today that requires it for scan to folder functionality.
Information about the update is published at: https://support.microsoft.com/en-us/kb/3161949
This update is a security update for WPAD. WPAD is a method for automatically configuring devices with a proxy server. However, as part of locking down this process, it does one critical thing. Here's the quote:
NETBIOS communication outside of the local subnet is hardened. Therefore, by default, some features that depend on NETBIOS (such as SMB over NETBIOS) will not work outside the local subnet.So, communication on the local subnet works, but if the MFP and server hosting the share are on different subnets then it breaks.
Fortunate the fix is pretty quick, add a registry key and reboot the server hosting the share:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NetBT\ParametersAnother Microsoft page that describes the same update, but slightly different description: https://support.microsoft.com/en-us/kb/3165191
Value Name: AllowNBToInternet
It's also worth noting that when troubleshooting this, the Security event log did not contain failed logon attempts for the user accounts. NetBIOS over IP was being dropped at the networking level and authentication was never attempted.