This looks like the error you get when you run the .exe outside of the folder. Try making sure that you are running the .exe through file explorer in the "KTool" folder?
Press Alt+Click on a key, door, or other object to open up a code editor. You have to set their variables with code to make them function properly, even single keys/doors, or else they break in the editor. How it typically works is you set variables with code formatted like "variable=value;", with the semicolon at the end of every line of code. The most common variables are "count" for key/door count, "w/h" for door width/height, "c" for door lock color, "cs" for door base color, and "type" for key/door type. You can read more about them in the instructions file attached.
Key counters work a special way. Basically, the counter itself is the "list" of key counts to show, and you add the different key colors to that list, which it then auto-generates the counter graphic with. The basic code looks like such "s0=COLOR;s1=COLOR;s2=COLOR;" etc, with each "s" being the first, second, third row of the list (starting from 0), and "COLOR" being replaced with a number which correlates to the key color, which you can find in one of the readme files. You can also set "long=(Either 0, 1, or 2);" to make the counter longer.