The purpose of this article is not to discuss a "wrong" call in the sense of a player not becoming exactly what I said he would be. The world of prospect evaluation is far too complex, and has such an inherent error rate with wild fluctuations in development, to be that narrow.
Instead I'm focusing on calls that were "wrong" in hindsight and had a clear reason why the call at the time of the decision should have been different.
For example, I had Colorado's Mikhail Grigorenko rated as a top-five prospect during his draft season. I do not consider that call as "wrong," even now. Given the same info at draft day, I would make the same call. However, a year or so later, I should have been somewhat more pessimistic about his prospect status.