After wrestling mostly unsuccessfully with Win10 issues, I ended up reinstalling both Steam and Skyrim, but now when I load the game, I get the message mentioned above, and big chunks of my game (houses, weapons, companions, etc) are no longer there. I am at the same level and location as my last save, but some important and aggravating-to-lose stuff is gone and I have no idea how to get it back.
I have not installed any mods or modified anything about the game other than what I purchased initially, which had the Hearthfire, Dragonborn and Dawnguard DLCs included.
Any advice welcomed. Thanks.