Hello, I was following the MED tutorial from the download page and it says, once you open the skin manager to go to Edit->Create 6 Sided Mapping. However when I clicked Edit I didn't find that option. Does anyone know why? Thanks in advance.

This option is located under
Object -> Generate Mapping -> 6-Sided,
not in the Skin Editor.

thank you , i found it, but it's disabled. do u know why?

2-sided mapping applies to the whole model, 6-sided mapping only to selected faces. If there is no selection active, this option will be greyed out.

thank you very much! xD