I'm guessing you already had the map terrain uploaded into the game. If so then when you tried to remove the virus, your computer deleted files or moved them. If the terrain.cfg suddenly went missing then try searching your recycling bin for it, or try opening up your FH folder and typing in the search bar terrain.cgf.
Now of course the terrain.cgf wouldnt be called that. You'd actually be typing in burial.cgf or whatever you named it.
If I was wrong and you haven't uploaded the terrain to FH yet then make sure it has these requirements from GIMP/Photoshop
-513x513
-greyscale
-no alpha channel
-"mapname"Terrain.png
