Do you still run a Windows 7 computer that has shared folders? If you do, and those shares are set up so that they require user authentication, and the user involved is a member of the Administrators group on the Windows 7 computer, then you may find that those shares stopped working recently.
This problem was triggered by one of the Windows 7 updates from January 2019. Uninstalling that update fixes the problem, but doing that also rolls back some important security updates. So that’s not really a viable option.
Thankfully, Microsoft issued a fix for the problem. I’ve tested this fix and confirmed that it does work. To install it on your affected Windows 7 computer, locate the appropriate update (KB4487345 for 32-bit computers; KB4487345 for 64-bit computers) on this Windows Update Catalog page, click to download it, run the download and respond to the prompts. You’ll probably need to restart the computer.
Born’s Tech and Windows World has additional details.