Source: my tv (Sky Sports News)
Something to do with reserve player Gael Kakuta and breaching a contract. Have to pay Lens £682,000 compensation (don't know if that's Chelsea or Kakuta that has to pay). Kakuta has been given a 4 month ban on top of it too.
The Guardian states:
Chelsea FC have been banned from signing any new players until 2011, after Fifa accused them of illegally inducing a French youth-team player to join the club in 2007.
Fifa's dispute resolution chamber today released a statement fining Gaël Kakuta €780,000 following a complaint from FC Lens and finding Chelsea "jointly and severely liable".
Continue reading the rest of the article from the link below
And more info here:
(thanks superelle07 elementarystars & malinowy )