I added a shadowvolume to a model that was working fine before, but then when I tried to munge with the model used for a weapon, it gave me this message "pc_modelmunge.exe has stopped working". The error appeared when it was making a hires shadow mesh.

The munge log gives these errors:
What do I have to do?

You'll likely need to rework your spear.msh. Go back in XSI and investigate the problem. You know it worked before adding a shadowvolume, so that would be a good place to start. Are you using ZETools? Make sure your mesh meets the requirements for it to export properly.