This is one of the many random & sporadic glitches present at chess.com
I'm getting the same message in both FireFox & Google Chrome Browsers.
You can try using them and IE8, and also see if you can get any other FEN string to work for now.
Make absolutely sure you are cutting & pasting the entire FEN string exactly and if it still don't work contact Help & Support and/or see my blog for other ideas, altho I'm not sure if any will help here
http://blog.chess.com/NimzoRoy/diagnosing-and-fixing-internet-problems
Hey Chess.com
Im trying to create a diagram with a game. However, the setup is different from the normal setup.
The game starts like this:
kqnr4/rnbb4/4pppp/4pppp/PPPP4/PPPP4/4BBNR/4RNQK w - - 4 1
When I post it into the diagram it says the FEN string is improper? How can I get it to be displayed?
And once I got the FEN, am I afterwards able to add the PGN?
Thanks for the help!