I just thought that I would post this here, as it may help others. I have a couple of PCs with Windows 7, both with shared folders that I access from my iPad and iphones via both FileBrowser and Readdle Documents. A very recent Windows security update, which I installed yesterday, has stopped access to the shared folders, even between the PCs, with a message to the effect that the handle is invalid. This is a problem that others are experiencing for both Windows 7 and 10. The update is KB4480970 or I think came to me as part of KB4481480. Uninstalling KB4480970 seems to have rectified the problem for the moment. I hope that this helps others who may have been as perplexed as me as to why I suddenly could not access the shared folders. Btw, I will post this in the sister iPhone/ iPad forum.