For the last couple of day, I have had difficulty trying to upgrade my Whatsapp to new 2.8.0.0 and yesterday with AirNZ mPass 2.0.0.0.
Both cases, the installation gets to 75% mark then reset and present to me "Attention required" message. However when I tried to install Viber (new to my account/device) it went through installation just fine.
Apparently this is a widespread issue:
http://answers.microsoft.com/en-us/winphone/forum/wp7-wpapps/apps-fail-to-install-past-the-75-mark/211c706c-dbb4-4a95-b4c2-aadb1d40f80f
http://wmpoweruser.com/windows-phone-marketplace-facing-app-updates-issue/