Microsoft KB4480970 blocks file share access on Windows 7 and Server 2008 SP1.
To resolve the issue it's a case of removing the update.
Do this by opening a command prompt as administrator (right-click, run as admin).
Then type or paste this line in and press Enter:
wusa /uninstall /kb:4480970
You'll be prompted to reboot after it's done its thing.
After the reboot, log back in and search for updates in Control Panel,
Find KB4480970, right-click and 'Hide Update'