Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Rush refused to put your holder in a place that already belongs to someone else. Here is the idea. A filesystem holder is a directory, and every member is a file that the holder itself wrote. Because of that, rush is careful about where a holder can settle. It will take a path that does not exist yet, and create the folder. It will take an empty folder. And it will take a folder that already carries the holder's own mark, a tag that rush wrote when it first declared the holder. But it will not move into a folder full of your photos, or onto a path that is a single file. If it did, the holder's normal writes could overwrite or delete things that were never its members. So it stops, naming the holder, and the second slot tells you what the path turned out to be. Say you pointed the holder at your documents folder. The fix is simple: point it at a new, empty folder, or a path that does not exist yet. Your files stay safe, and the holder gets a home of its own.
Text from the Rush engine's error catalogue.