Since i joined the Emperials, i like to go to stormcloak camp's and start some havok there..

But i found out there is always 1 guy who always get up. I cant kill him.

You guys have any clue why?

He must be essential.But it shouldn't be a problem if that's the case.Can you not continue on with the quest?

Maybe you can open the console,click on him and type "kill" without " " but I don't know if it'll work or break some other quest.

Its not part of a quest. When i travel form A to B i never fast travel. When i see a stormcload camp, im going there to kill them.. But ive noticed that there are Stormcloak members who cant be killed somehow.

Its an issue with the fact the game doesn't unflag them as essential when you join the Legion. Legion/Stormcloak quests mirror each other, so those guys are basically the same as the quest givers at the Legion camps.

It shouldn't be an issue, you can just leave the area once you're done. But except for the use of console commands, you're not going to kill them.