Recently all of the entries in my iphone (4s) calendar appeared to disappear, both on the phone and on the icloud. However the entries are still there but are not visible. I verified that the entries are still there by installing a third-party calendar app and syncing with my iphone calendar. The entries are visible in the third-party app but not the iphone. What can I do to fix this so that my entries are visible in the iphone's calendar?