Whether Minitab draws the plot depends on the degrees of freedom for the error term. If the error term has 0 degrees of freedom, Minitab does not draw the plot.
Minitab plots the normal scores, probabilities, or percentages versus the standardized effects. The line corresponds to a normal distribution with a standard deviation of 1. Effects with p-values less than α are labeled significant on the graph. Minitab labels the graph Normal Plot of the Standardized Effects.