interesting crash... i would recommend to not use the add stencil feature... use the mudbox image browser instead... just navigate to your image and click the set stencil icon in the image browser...
I'll have to try that. For now, I believe I found a workaround. I've used a directory full of images that I migrated from my main texture library to pull into Mudbox via a Window 7 library to reduce clicking time. When I grab the textures I want and just move or copy them into a folder that's not full of images, such as…