It sounds like some of your files for FH are a bit corrupted, I'd recommend deleting FH and re-installing it.
Since you're a map maker, to save your maps, copy and paste your 'Terrains' folder, your 'Objects' folder, your 'Music' folder and your 'Sky' folder into a seperate folder in the C:/ drive so that your meshs, heightmaps, sky/weather, music and object placing will stay the same. Once you have re-installed FH you can just put the folders back to where they go in the FH folder and make sure to replace. You won't lose anything from your maps then. x3
Basically, if you want to save any files, just copy and paste them to a different folder then replace later on.
Hope I helped.