Check the output again and make sure it is extactly same. In my case, i have renamed qtree which i created intially because of the typo but the quota policy rule was showing the old qtree name. I have deleted the old rule and i am able to activate.
Second command will display the extra qtree listed as root. I think it is normal
Sorry, I forgot to update this after fixing the problem a while ago.
For the benefit of others experiencing the same issue, I had two quota policy rules that were referencing the qtree's by the path rather that the qtree name itself. I removed the quota policy RULE and recreated them by referencing the qtree name. I was able to activate the quota on the volume after this.