If the disk has any other name, it will not start up: the program gets to the "Welcome to MousePaint" screen and then scans down to the Disk IIs that are connected. When it comes back to the 3.5-inch drive, it gives an error message "Path Not Found". The next line says "Break in 10" and displays the bracket prompt.
Another solution is to set the pathname in the startup program MP.START on the MousePaint disk. Either of these solutions works; the first is easier.