Well, I know just what you mean...
I try to turn of everything but the camera, some emitter and perhaps the floor or backdrop and then I write a MXS file, ok no crash, then I try to render the scene, ok no crash, then I add more and more objects and repeat the process with writing MXS and rendering. About now one would have pinpointed the problem... Don´t forget to save after every change to the scene.
Another hack is to create a new c4d document and copy the contents oft the "bad" doc to the new one, except the "maxwell render settings object".
I try to have all the textures in the same folder as the c4d doc.
I try to keep every bitmap as a RGB .tga file or hdri
Beware of too long path names.
I really hope this alpha/beta behavior will cease to exist.