The Wall Street Journal reports that Green is taking a leave of absence for medical reasons. They quote Tomi Kuuppelomaki, a Nokia spokesman:
"Rich Green is taking a medical leave for absence. During this time Henry Tirri, head of Nokia Research Center, will be the acting CTO."
A report in Helsingin Sanomat, suggests that differences over software strategy may have contributed to the departure.
"Green's [departure], at least partly related to differences in the decision to give up MeeGo partner, Intel. According to one interpretation, Green would have liked to continue the development of MeeGo".
Prior to the February 11th announcement that Nokia would partner with Microsoft and adopt Windows Phone 7 as its primary platform, MeeGo had been thought of as being Nokia's next generation platform. After this time, MeeGo was relegated to “Future Disruptive Technologies” and head of MeeGo Computers, Alberto Torres, “stepped down from the management team, effective February 10 to pursue other interests outside the company” (source: Nokia Press [PDF]).
According to an extensive interview with Stephen Elop by Business Week, Nokia were on course to only have created three models of MeeGo handsets by 2014, which was too slow to facilitate the company's turn around.
Meanwhile, as CTO Rich Green was responsible for overseeing the future direction of Nokia's future development, including technologies including Qt and MeeGo. Given the depreciation of Nokia's major software platforms, the role of CTO has been understandably diminished. Nokia's best hope of a come back is through continuing its expertise in hardware. It is reasonable to assume that the this change of focus will be reflected in the activities of Green's replacement.
Here is Rich Green talking earlier this year about the future of Qt:
David Gilson for All About MeeGo and All About Symbian, 9th June 2011