Why is this mirror object not reflecting light onto another surface properly? I have a scene where the sun rays should be reflected from a mirror to create this sort of effect:



The problem below was resolved, scroll down to EDIT.

However, I can't get any light reflected from any glossy surface. I set up a simple scene to test it ans here is my result.



And here is rendering.



But the cube stays dark.



I will be very happy if somebody could help me with this.

Blender file:


EDIT:



I fixed the problem with the test file by adjusting light position and size (and maybe something else). For that I added a ground plane and was adjusting the parameters until I got the shadows right. 

Increasing the roughness parameter, suggested by Duane Dibbley makes rendering faster and less noisy. However, then it is not a mirror any more.  When the roughness is zero, rendering takes a lot of time and doesn't look like it is going to finish.
The roughness setting is insanely low, which makes the reflected light beam very narrow. If you increase the roughness, the light will be spread in a wider beam. This will, of course, also make the reflection of Suzanne somewhat blurry. In the image I've included, I have it set to .1, but I also tried .01 (10 times the .001 you have), and that made the interior of the cube visibly brighter.