Currently, the G6 character is classified as non-standard character. Thus, you cannot add a custom face to them.

An updating G6 character which enable more functionality will come in a future update.
http://www.reallusion.com/iclone/iclone_ComingFeature.html

For the moment, if you wish to create a custom face, please load G5 character either Chuck or Gwynn. Then the "Create Face" features will become active.