Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Your range has a step of zero, and rush stopped it before it went nowhere forever. Let's think about what a range does. You give a start, an end, and a step. Rush begins at the start and walks toward the end, taking one step at a time, and collects every number it lands on. With a step of one, from one to five, you get one, two, three, four, five. Now imagine the step is zero. You stand at one, and every move takes you to one again. You never reach five. The walk would never finish, and the list would never be answered. Rush could return an empty list, or an endless one, but both would be inventions, so it refuses by name instead, and the second slot repeats the details. Where does a zero step come from? Often from a calculation, such as the difference between two values that turned out equal. The fix is to guard against it, check that the step is not zero before you call range, or choose a step that actually moves. A walk needs a direction.
Text from the Rush engine's error catalogue.