Someone above mentioned waiting for all your characters to load in their portraits. I tried doing that as I was playing and I noticed something, when I get the error, there's always one character in particular that fails to load.
To describe it better, at the character select screen, the portraits for all my character will start loading in from left to right. If that character portrait loads, everything will be fine and I'll be able to select the next character as normal. If their portrait doesn't load, the next 2 or 3 portraits will load, but all the others won't, and if I try to play another character I'll get the infinite load.
I'm reasonably sure it's not the class, but it might be the elite spec (willbender). It might be something to do with the character's appearance (gem aura outfit). I've switched another character over to have the same outfit, but the issue hasn't reoccurred yet.