Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Rush found a step that had lost its place. Let's see what that means. Many steps in rush work through something piece by piece: the bytes of a text, the members of a collection, or the stages of a longer job. To remember where it stands, a step keeps a cursor, a simple marker saved with the step's working data. Every time the step resumes, it reads the cursor and carries on from there. The cursor must always point somewhere real. If it is below zero, or beyond the end of what is being walked, or past the last stage the body has, then it points at nothing, and the step cannot know where to continue. A guess could skip data or repeat it. So rush stops, naming the step, and the second slot shows the test that caught the cursor outside its bounds. Think of a bookmark that sits past the last page of the book. This is a defect in the step's own logic, not in your script. Report the message, and the cursor can be corrected where it goes wrong.
Text from the Rush engine's error catalogue.