Finally it worked .. I clicked on the mammoth even though the attack icon was there, I mounted it and was able to complete

have used the harness many times only to still get an attack icon .... no mount icon appears

http://www.wowhead.com/quest=12607
When I use the mammoth harness on shattertusk mammoths nothing happens

http://www.wowhead.com/quest=9361

i collect the tainted meat and use the purification mixture on it to only find that the tainted meat has disappeared and i have no cleansed meat. I have went through approx 20 meat this way so far and nothing.