Try a different graphics driver. There are a few in the same directory which you can replace in the ini file which the kit creates on the first start.
Those drivers came with an old Pascal version, and are rather buggy, unfortunately (other software using them have the same issues).
You can also try different mouse drivers.
In many cases, the EGA driver is the only one working correctly. You still can use the editor with it, except it won't display the correct colors of the cave.
Also keep in mind that the kit itself is early beta and not bug free either. And I have no intention to work on that one anymore.
The CLCK has the priority for now. And after that, I have plans to do a new engine which shall feature the best of The New Dash Dimension and Boulder Remake, beeing compatible to every version of the C64 engine and natively using BDCFF. As it should be portable C or C++, so it can be easily ported to handhelds as well, I have to rewrite it mostly from scratch. Thus making it the perfect clone.
Anyways, nice to see that people are still playing The New Dash Dimension today.
