If you visit the Learning Center and look at the information about the Mobile App it shows the following requirement, “_ Android smartphone or tablet running versions 2.3 or later software _.”
When I noticed I could no longer use it I went to download it again and found the following information. See image below. My phone has Android 2.3.6.
From the date shown it was updated on Sept. 3, 2014. If the OS requirement has been changed it should be reflected in the Learning Center Information.