I've got this bug on both the PC and Mac and I've never found a way to get it going. Just like you, on both platforms, B6.1 is not hung 'cause I can click out of the render. Saving and resuming doesn't seem to be working either. It's been mentioned that turning off 48-bit dithering and re-rendering can solve this,but that's not working for me. The way I'm working around it is to not use Normal AA and using 16RPP Premium mode. MacPro/10.4.7 and Pentium D WinXP.