From Times Online:
Vatican sources said that tensions had been exacerbated because the Pope had written the first part of the encyclical in German during his summer break and the second part was an adaptation of a document left behind in Polish by the late John Paul II. It had been passed to Vatican specialists for further revision but remained unfinished at the time of John Paul’s death ten months ago. The two parts had had to be “harmonised”.
The Pope, responding to growing speculation about the delay, told pilgrims at his weekly audience yesterday that the release of the text, originally planned for early December, had been delayed until next Wednesday.