Hmmm, I tried to recreate your error message, and I can't.
So, my first question would be: What Version of CC3 are you running? I currently have version 3.22 (downloading 3.24 now).
Another thought is this: Right Click on the FLOOR TOOL button. The pop-up should display Floor Samples and state it's STYLE is Dungeon DD3 Color.
If not, then likely something is happening when you click on the ADD CORRIDOR button to deselect the DD3 styles.