From my thread on the same topic:
So I had this same issue with Tweetium (given its recent update on the front page of Windows Central). I did some more digging around the web. I found a thread at the Microsoft Communities forums for Windows Phone that had a suggestion to log into
https://account.microsoft.com/devices and remove the affected phone from the account. The forum entry says to immediately resync the primary Live ID on the phone via email+accounts but that is unfortunately inaccurate. The process that worked for me was similar but involved:
1) Log into
https://account.microsoft.com/devices
2) Remove my Lumia 1520 from my Microsoft Account
3) Reboot the Lumia 1520 (this is the missing step)
4) Sync the main Microsoft Account after insuring that "Find my phone" is enabled on the phone.
5) Now attempt to download the update from the store.
The above 5 steps resulted in my ability to download the app without further issue. This may not fix the problem for everyone, but it's worth a try since it is actually harmless.
Good luck to all!