Rays Halting Unexpectedly

Sometimes rays unexpectedly halt on a surface. The picture below shows a single ray bouncing inside a perfectly reflecting cylinder, but surprisingly stops.

Raytrace Summary

In simple scenarios, looking at the Raytrace Summary that is automatically printed to the Output Window might give you all the information you need. The clue to this problem is in the line "Num rays halted due to exceeding number of consecutive intersections on the same surface."

Table of Ray Errors

In more complex cases, it might be more insightful to view the Table of Ray Errors report located under the Tools menu. This logs all ray errors on a surface by surface basis. 

The Solution  (in this case)

In this case, we need to increase the relevant cut off in the associated Raytrace Control, to allow the ray to reflect off the same surface consecutively more than the default 10 times.