This error notifies the user that their nozzle design is beyond the curve boundaries of the WRC standard (107 or 537) and the nozzle parameters need to be modified to fall with the scope of the standard.
WRC has stated that if the design is outside the curve boundaries that WRC 537 is not valid for use.
See the demonstration below:
Figure 1C has some extrapolated values below. When the WRC was asked what the correct value of Y, when gamma = 50 and beta = 0.45 ?
We asked if we could use the Y value obtained using the equations and coefficients from WRC 537 which is 0.194
We asked if we should use the last known data point for gamma = 50 which is 0.05 (which competitive software does to just to get a stress value to plot out).
WRC's response was that we should not use either option because WRC 537 cannot be applied.
To help get your design within the scope of WRC, you can modify the mean radius of the shell, the shell thickness, or the radius/perimeter of your attachment.