Each time I have logged into the MP system, it has asked for my Serial Code. Anyone else having this problem or not what I need to do to get it to stop. Once I enter it, I get in fine, but when I exit and go in again, there's the prompt again asking for the code.

You only need to enter your keep once. You are entering your key at the wrong location.
The place for you to enter your keep is located at the sign in screen for the game. Which is the first screen you get to. Hope that helps

Same here. I have put my key in to the initial log in screen and the multiplayer screen. Every time I exit the game it seems to reset it and asks me for it every time I want to go to multiplayer. If someone could post a fix for this I would be grateful.

I see the field to enter it on the first login screen, but it does not save. I have 'save details' selected, and it remembers my Username and pw just fine, just not the code. Switching from MP to SP and back again, or exiting and rejoining MP requires reentry of the code.

I see the field to enter it on the first login screen, but it does not save. I have 'save details' selected, and it remembers my Username and pw just fine, just not the code. Switching from MP to SP and back again, or exiting and rejoining MP requires reentry of the code.
Same exact thing for me. I really hope this is an EA/Crytek issue that will be fixed immediately.

same thing here

It's working now.

You guys get "Serial Code is in use." error when trying to join a multiplayer server? I tried everything and this is a legit pre order copy. Man i'm so disappointed. I'm not giving up.

this is a known issue that will be fixed soon, the same applies to your issue pcnuttie.

I forgot that Crytek's based in Europe. Hopefully both of these issues will be fixed before I get home from class tomorrow.

this is a known issue that will be fixed soon, the same applies to your issue pcnuttie.
Thanks for the reply Tom.