Problems loading blockchain from existing folder
As far as I am aware, you will also need the chainstate folder in order to properly run from a backup. Other files/folders are not strictly needed to restart your daemon. More information concerning specific folders can be found here: https://en.bitcoin.it/wiki/Data_directory

If all else fails start the process with -reindex and let it run - it "only" takes 24-48 hours depending on your bandwidth. Even though I know you don't want that!