been getting this for the past 2 weeks since reset.
happens when i am in a 5man/raid group, any new instance, raid or dungeon when i try to zone it happens. it can even happen when i take the portal to uldum from orgrimmar or stormwind
best case scenario i log off and log in it works.
Just got the same issue and it kicked me off my taxi flight near the burning steps. No groups or anything, just flying.