Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You wrote a short name for something outside your scope, and it turned out to be ambiguous. The idea is that you write a name with the least information needed to find it. Often, one module segment is enough. But what if two different things end in the same short name? Then your qualification points at two places, and the engine cannot choose for you. Guessing would be dangerous, because the program might call the wrong function and still seem to work. So the refusal happens at parse, before anything runs, and the message names both candidates, so you can see exactly what clashed. Imagine two people named Maria in the same office: calling out Maria does not work, you need the last name. The fix is to add the segment that tells them apart. Write one more module name in front, and the name becomes unique. Then the parser knows precisely which one you mean, and the guesswork is gone.
Text from the Rush engine's error catalogue.