Note that if you change the path for your User Data Folder, you may also create this problem. You can change that path in the serverconfig.xml file, in your shortcut, or in your Steam Properties for the game. If you change it to a folder that has paths, it is required that you use quotation marks or apostrophes around the path (I'm not positive which is used in this game, but probably apostrophes). Otherwise, it assumes the part leading up to the space is the path and not the entire thing. That means if you're trying to save to a Program Files folder, you're going to get C:\Program\ as the path.
You can correct this, regardless of the cause (other than if you're using Vortex Mod Manager) by setting a User Data Folder somewhere without a space or by using quotes/apostrophes around the path, even if you want to use the default location without having to completely nuke the game. You'd need to manually move any mods/saves/maps/etc. to the correct location, of course. If that doesn't work for some reason, then nuking everything is the easiest option.