New scene, add cube, add sun, set IR max passes to 20, start IR in the VFB - hits 20 and stops as expected, no crash. Change something in the scene, re-renders up to 20 passes and stops normally, and so on. Did you send in the bug report.txt? Always send in the bug report.txt for a crash :) Also, which OS, which version of C4D, and when you say "latest daily build" best to put the date juuuust to be sure we know which one you mean (I was using the Oct 23rd daily build).