Since the official support is CRAP...Follow

Marty: Thank you for contacting Turbine Technical Support. Which game can I help you with today?
Pawkeshup: LOTR:O
Marty: How may I help you today?
Pawkeshup: Every time I get into the game, the client keeps registering the S key as being depressed.
Pawkeshup: So I'm constantly moving backwards and unable to chat
Marty: Could you please elaborate your issue to me?
Pawkeshup: If I try to move forward I cannot. As you know the default movement key binding for backwards is S
Pawkeshup: And if I hit enter to open the chat box, it just fills with the letter s
Pawkeshup: I know it sounds odd. As you can see the S key works fine in everything else.
Pawkeshup: The window did lose focus briefly to another application. However I've restarted the computer and the application a number of times.
Marty: Pawk, I will suggest you to please try running the game either from a different PC or after changing your keyboard. In case , if you still face a problem after that, please let me know.
Pawkeshup: Ok, it's not the keyboard and this is my only computer
Pawkeshup: If it was the keyboard I wouldn't be typing at the moment
Pawkeshup: And it's been working fine until today.
Pawkeshup: Is there some way to clear up the repeated input?
Pawkeshup: Still with me Marty or am I disconnected?
Pawkeshup: It's been over 5 minutes, are you still there?
Marty: Sure Pawk. Could you still please let me know since when are you facing this problem?

Pawkeshup: Since this morning when I tried to play.
Pawkeshup: Is there any other information you need?
Pawkeshup: Well, since you're not responding I'll just give you the complete play by play and it might trigger something in your searches.
Pawkeshup: I was running to find a quest NPC with Autorun active. While I was running SpySweeper popped up a window through the client interface just as I went to close a bag.
Pawkeshup: It caused me to go to the desktop. I clicked back onto the client and tried to stop moving forward. And then I wound up walking backwards.
Pawkeshup: If I auto-run I can move forward but I can't walk normally nor type.
Pawkeshup: So I figured out that the client is registering an S consistantly. In WoW I'd normally do something like a UI refresh to clear the issue, but I can't type.
Pawkeshup: So what I need to know is why it's registering this, why ONLY this application is registering it.
Pawkeshup: Hopefully that gives you a little more information.
Pawkeshup: I've tried rebooting, I've disabled anything related to any form of input filter.
Pawkeshup: I assume you're having issues finding a solution and I don't blame you, I work in tech support and I haven't seen something like this happen. I've seen some controllers like Analog sticks do this when their centers are not set proper.
Pawkeshup: Now while you search, since it's lunch here, I'm getting some of the food I have waiting for me downstairs. I'll be back in 5 minutes. Since I've been waiting almost 10 minutes since your last message, I hope you will understand and wait at least that 5 for my return.
Marty: Soory Pawk, I will suggest you to please contact again, as we will be here always to assist you.
Pawkeshup: Ok I just came in to check. So you don't have any ideas?
Pawkeshup: So far you haven't suggested anything aside from try again later?
Marty: Pawk, I am suggesting you to please try running the game from a different System and let us know whether you are facing the same issue or not.
Pawkeshup: Ok, so you want me to go out, buy a NEW computer to test this? What kind of troubleshooting step is that?
Pawkeshup: It worked just fine on this VERY computer, the one I am using to talk to YOU now, and as you can see the chat is not full of S's right now, you'd agree to that I assume...
Pawkeshup: So, since this is my VERY first experience with your tech support I'm to understand if it's an issue you don't know about you're going to tell me to try another computer?
Marty: If in that case you face the issue again, please let us know. We will definetely assist you to the best of our knowledge.
Pawkeshup: I'm still facing this issue!
Pawkeshup: You haven't fixed this issue at all!

In your PC, go to the following directory - "C:\Documents and Settings\your user name\My Documents\The Lord of the Rings Online" and look for lotro.keymap and UserPreferences.ini. Delete these files then relaunch the game to see if that helps. These are the settings for your keymapping and keyboard shortcuts etc.

Did anyone tell Marty? :)