It would appear that the Blackwing Descent raid portal is bugged and not letting people enter the raid. I tried for about 10 minutes to enter the raid via running into the portal. I logged out and back in, exited the game completely and came back in, formed a raid group and tried walking in, changed the difficulty from normal to heroic and back to normal, changed the number of players for the raid and thus far nothing has worked. I also watched someone else a Druid on Korgath also struggle with this bug. I also checked and have not found anything on the forums about this being a known bug.
I’m having the same issue today. On Eonar. I submitted a bug report but still sucks cause I came all the way out here and was reading to do some achievements.