When the axis equal error comes

When I use the 'axis equal', the error comes as follows:

" Error using matlab.graphics.axis.Axes/set While setting the 'PlotBoxAspectRatio' property of Axes: Input values must be positive finite numbers.

Error in axis>LocSetEqual (line 388) set(ax,'PlotBoxAspectRatio', ...

Error in axis (line 131) LocSetEqual(ax(j),pbarlimit);

Error in display_3view_initial (line 21) axis equal;colormap(char(ColorMap)); "

However, when I use the 'axis auto' or 'axis image', there is no errors. Does anyone know what happens here?

[Guanfeng Gao]

I go to the error line and fine that when execute the line: " set(ax,'Units','Pixels'); a = get(ax,'Position'); " The result is a=[1,1,0,1], here a(3)=0, which induces the error. However, the a value is obviously wrong!!!! And the get function is the matlab build-in function which I could not read the source code!!!!

[Walter Roberson]

Are you using dual monitors?