How do I find the "FEN string"?

I keep copying it from the original game (which was a live game), but it says that it is invalid.

Suggestions?

I thought FEN strings corresponded to a single position...though I'm not positive.

When I want to post a game, what I do is go to the game in my archive, select all the moves, copy it. Then go to the game inserter and paste it in the PGN file location. And there you go. Hope this helps.

yes you need the PGN for the actual game, the FEN is for a certian position

once you click insert board, then click on game/sequence, then add the PG, add notations if needed, and click insert.

You can access your Live Chess games at http://www.chess.com/home/my_archive.html?show=live and then once you view one of the games you can click on the "details" tab where you will find the FEN string for that specific position of the game you are viewing.