The reason the symbolic link fails to be created is because the user mythtv is not on the sudoers list by default.
You can add mythtv to the list by editing the /etc/group file just add mythtv to the end of the "admin" group seperated by a comma
Example
admin:x:119:jamie,mythtv
Hope this helps simplifies things for people. The mythtv can be removed for the admin group once shepherd is installed if you wish.
Jamie.