eagle generate multilayer gerber file
Hello,
I'm not particular familiar with eagle, but with most cad systems, the postprocessor does not automatically generate the necessary apertures. You must first issue a command like "check for missing apertures" or "generate apertures". After that step, the gerber files can be produced.
This is cause old style photo plotters had an aperture wheel with certain well-defined apertures, but had been unable to use arbitrary apertures as todays laser plotter. With these old devices, you had to load an aperture definition from the PCB manufacturer and take care, that no unknown apertures would be used.
Regards,
Frank