Well I am lvl 34 and am unable to continue the quest at Thalmor Embassy.

I have a feeling this bug relates to me killing Thalmors inside there embassy before this quest was started. I would say around lvl 30 I ran into the embassy and decided it was a good Idea to kill everyone off within it with my bow . I have finally continued with the main quest and have been brought into the Embassy. But I can not gain access to the Embassy building which is locked. So basically I can only run around in the front court yard and look at the bodies of the dead thalmor's that I killed earlier in the game. This is a major glitch because this means I am unable to participate further in the main quest unless I can find a quick fix or a patch is released. Not sure if anyone can comfirm that the killing of Thalmor NPC's within the embassy before starting the quest can cause this bug or if it is other issues. I have fully completed the main questlines on another charactor.

I dont remember very clearly, but did you get the invatation and give it to the guy at the front door?

The invitation is given to whoever when you enter the building I think. Which is suppose to be unlocked but in my case it is currently locked so I can not enter without a key. But right now it is just me, 3 carrige drivers, Razelan who is sitting on a bolder and keeps repeating "please take your time I will go after you......." and the dead bodies of 2 thalmors that I killed by shooting them with a bow through the gate earlier in the game before starting "Diplomatic Immunity" So right now i have not heard of it just getting bugged and not working. So I am guessing it may have to deal with killing people within the embassy before the quest. I am guessing I am probably one of the only ones or one of the very few that have done this so theirfor it may never have been brought up yet. Or I could be wrong and just bugged in another form. Just trying to give Bethesda something to test that could bring up the bug.

Edit: You could be right and then basically the person I am suppose to hand it to is dead and therfore I am unable to hand my invitation to him and well he will not unlock the door for me. :/ darn it anyways lol. looks like I am stuck running around doing other things besides the main quest untell a patch comes out or I find a way around this problem