I'm having exactly the same problem. As soon as i click 'upload/image' it 'whites out' on FS and crashes on LL viewer. This started yesterday afternoon, up until then it was working fine.
I've deleted my cache folder, reinstalled viewer, tried different sims, different avatar, different computer ! but still cannot upload, it crashes every single time.
This is extremely frustrating, and I have no idea what to do to fix it.