I had similar problems both times I upgraded. I tried various things until things worked. These seemed effective for me:
– hold reset button for 5 seconds
– uninstall the app and reinstall the app
– batteries out and back in.

Also, it seems that whenever you see a upgrade progress appear to complete, and yet the Mooshi still shows the build number on the Scan screen, it does not mean that the upgrade did not work. Because doing one/some of the above steps will cause the Mooshi to then show up with the new build number.