Recent KB4480970, KB4480968 updates for Windows 7, 2008 r2 server are breaking access to SMBv2 shares.
The fix is a registry entry (run in 'cmd' as administrator):
reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\system /v LocalAccountTokenFilterPolicy /t REG_DWORD /d 1 /f
The effect is immediate - no reboot required.
Alternatively, install this later Microsoft Update (KB4487345) to fix the problem:
- https://support.microsoft.com/en-us/help/4487345/update-for-windows-7-sp1-and-windows-server-2008-r2