I have windows 10. Every world file and save file the game generates has ".new" appended on the end (world.rww.new or save.rws.new) Once I manually delete the .new the game recognizes them just fine and everything seems to work normally. But of course it would be nice to not have to do this manually every time I want to fire up the game.
Sounds like the game is have issues renaming the "new" files. Are you forcing a different save location with strange security permissions?
Possibly related to this bug report.
https://ludeon.com/forums/index.php?topic=19613.msg224410
I've seen this crop up a few times now, and every time RimWorld was running on Win 10 (I think). I blame Microsoft. Correlation = Causation, right? :P
There must be something funky about their file permissions.
Im on windows 10 and have been for a while now (for the last 2 alphas at least) and never had this. So if it is windows 10, its something that doesnt effect all users.
See my response here: https://ludeon.com/forums/index.php?topic=19613.0 (https://ludeon.com/forums/index.php?topic=19613.0)
Should be fixed in the next release. Locking.