This solved my problem. Icloud/Iphone connection was lost and would not update calendar or tasks. Problem seemed to have started with latest upgrade to Iphone. Anyway the reset instructions above did the trick. Thanks!
I'm having this issue I have an iPhone 5s running ios 8.4 this did not work for me. Any other suggestions? I need to back up this phone because I've made changes since my last update and need the preserve it.