I have no idea what I'm doing wrong....but I can't mount those stinkin YAKS! Friends have told me you just run up to them and right click them (which I'm sure is correct). However... I have no mount up button to hit...just the normal cursor. I've dropped the quest multiple times and still the same thing.
You need to use the rope that you got from the grummle and use it on the yak, once u do it they will be like smelly yaks or angry yaks and so forth. You will have to keep doing it till u get the right 1 which u can tell by the name of the yaks getting bigger and having more names in it like an angry smelly yak and so forth. The quest isnt bugged its just time consuming.