This happened to my guild (Imperial Outcasts on The Shadowlands) during an EC SM run on Tues 7/17. We made it all the way to Kephess and wiped on our first attempt. Some folks zoned out to respawn while some of us who died in the corner waited for a rez when they came back in. The folks who had zoned out were unable to get back in and received the above Server Admin error. We all zoned out at that point and none of us were able to get back in (all receiving the same error).
After attempting to get back in a few times, members of the Ops group starting DC'ing and were kicked back to the server select screen. At this point, when they logged in, they were on a silver and grey checkerboard out in space surrounded by the Imperial Fleet ("SPAAAAAAACE!"). They had to run to the edge of the checkerboard and jump off, fall for a fairly long distance, die, and respawn in the museum on the Ziost. I had logged off for the night as I had been DC'd and when I logged in the next morning I was on the checkerboard as well.
Since respawning in the museum I have not had any issues but we have not tried zoning back into EC. I opened a CS case and was told to use /stuck to fix my problem. Pretty ridiculous response (but unsurprising). I really hope that the Devs are aware of this issue and work to resolve it. Not being able to run Ops or running Ops with the constant fear that it is going to bug out on you is a huge disappointment.