The left arm appears to be all around larger, like a scaling issue is occurring just for the left arm. Where you can enter the console and type "setscale 1" to change overall body size ranging from 0-10 (i wouldn't use 0), the scaling for the arm doesn't match up. My simple test to see if it was a "man" arm was to load an armor mod that doesn't have a male form, which would logically cause the arm not to show up if that was the case. The only thought i have is that some coding is messed up somewhere, whether for 64bit or windows 7 (which i am using now). The issue doesn't appear for me on XP sp3 32bit (which i had before).