This will be fixed in the next release, and is specific to the 64-bit Windows version. The suggested workaround is to use Edit/Copy to copy the bitmap to your favorite program. I also suggest using the modern MRIcroGL instead of the aging MRIcron. I am happy if you find this tool useful, but most of my research efforts are focused on tools that leverage modern hardware (MRIcroGL/SurfIce).