I can see the logic in what @lutter suggests.  I don't think your change achieves that, though.
The way to fix it is going to be "use the correct task name" 99 percent of the time; the best improvement to usability would probably be [a double metaphone style algorithm](https://github.com/threedaymonk/text), though that is obviously limited to English and dialects predominantly, to suggest an approximate match.  (Levenshtein distance might also work as a fallback in the case of a sound-similarity mismatch, or to handle typos.)

Anyway, the core of the point is that mentioning directories doesn't guide the user to solve the problem any better than telling them the task was not found does.  The solutions are going to be either (a) fix your type, to the correct name, or (b) fix a broken task definition to work.

The one possibility that might enhance this in the transition is to check for, and report, an "old style" task matching that name specifically.  (eg: the older ${name}.yaml file exists, so we emit a message pointing to how to upgrade that to current standards.)

You might also eliminate some errors by including the search path in the error message, since that would highlight the failure of "threw it in /etc/razor/tasks, but that isn't on the search path"