Hi, This is due to API changes in libmate-desktop 1.10. You just need to wait for mate-screensaver 1.10 to migrate to unstable and testing - it will be built fine against libmate-desktop 1.10.
- Bug#796452: mate-screensaver: FTBFS: error: too... Chris West (Faux)
- Bug#796452: marked as done (mate-screensav... Debian Bug Tracking System
- Bug#796452: mate-screensaver: FTBFS: error... Vlad Orlov