The first time trying to launch the game after maintenance(just a moment ago, I just got home from work), I got the same error.
After closing the launcher, and immediately trying again, I got in.
Lucky me I guess?
I just did this for my guild.
The final rock wasn't clickable for me at first. I switched instances, and was able to click on it.
The chests and the datacrons were there, and it appeared that we got the Codex entries for the datacrons. However there was no stat increase, and the codex entries actually didn't show up in my list of datacrons.