I didn't see a bug report forum so I am posting here.

I have tried to enter the instance many times for the quest "Battle of the Gauntlet". Every time I go through the green shield into the instance, I am placed back before the green shield; I can't get in. I quit the game and logged back in, I also rebooted my PC. I even logged into another character then back into this one..... nothing works. I can't continue the Class quests until I complete this one.

Do you have a non-class companion out?

You need Yuun there, you should get a message with another Trooper companion, but companions that were added after release can cause weird behaviour in class quests.