Eigenray search by Regula Falsi detected a returning ray at angle 0.523599.  
Returning eigenrays can only be determined by Proximity.

You are running an eigenray search, or arrival pattern case using the Regula Falsi method (options ERF or ADR) and a backscattered ray was detected. This method only works when no backscattered rays are present, so this error message is shown.

• Choose an output option based on the proximity method (EPR or ADP);
• Try adjusting the source's aperture so that the rays don't hit the reflecting slopes;
• Another possibility is to not launch the rays at angles which result in backscattering, ie, instead of launching 5 equally spaced rays in the range [-45º, 45º], specify the launching angles manually like [-45º , 0º, 25º 30º 45º ].