Feldon An unintended effect of the August 26th Hotfix is that Quest Sharing is now completely broken. With the exception of daily Missions, quests of any kind and any level cannot currently be shared. The window appears for the other player, and they can click Accept, but the quest never gets added to the Quest Journal.
UPDATE: This issue will be addressed in a hotfix Tuesday morning.
Just a quick FYI: Rothgar now has mentioned in the thread that there is plans for a small hotfix for this next Tuesday.