There is a line towards the very top of the config.txt that is responsible for this. It tells the editor and engine where to find the art that is called for in the design that may be missing from the design folder, i.e. to look in the Default Art folder.
It will read something like:
Default_Resources = C:\Progra~1\DungeonCraft\DefaultArt
I don't recommend deleting it, instead put // at the left of the line to make it a comment. You can see that many lines in this sectin of the config.txt are commented out.
