Details

This message is generated when an element that is not a real number is encountered while shading contours for a ContourGraphics expression.
This message is usually accompanied by other messages that are generated when contour lines are computed.
Contour shading is controlled by the ContourShading option, which is True by default.
The first argument in ContourGraphics is expected to be an array of real numbers.
This message can result from evaluating ContourPlot or any other function that constructs a ContourGraphics expression and causes contours to be computed for that expression.
Off[message] switches off the message; On[message] switches it on. For example: Off[ContourGraphics::ctsm].