Wallet was using an internal data base that it’s not going to be supported by Windows phone 8.1 and Windows phone 10, then it must be migrated.
if you install last version of wallet version 3.0.0.x and you get a error saying that you have an invalid format of wallet data, it means that you need to migrate data manually. Notice that this migration is performed automatically changing password with previous version of wallet 2.x.
1.- If you don’t have any backup, please perform an emergency backup. This option is enabled on login screen when the problem is detected.
If you have a file with .sdf extension in your OneDrive, then it means that you have a not migrated version of wallet data. Then you need to migrate.
In order to migrate your data, please follow next steps:
1.- install Wallet lite from here http://www.windowsphone.com/s?appid=15f76158-39ef-4754-a773-cdc3dc7a5462
2.- Start Wallet lite application, setting a new password (for exemple 1111)
3.- Go to Settings screen and perform a restore from backup
4.- wait until restore has been finished, if everything goes well, wallet will start again and it will ask you for your old password.
5.- Once inside wallet lite with old password, check that all your data is there
6.- go to Settings and change the password (you can put the same). This is necessary in order to migrate your data to new format.
7.- Once change password has been finished, enter your password again and go to Settings screen and perform a backup
8.- When backup finished, go to OneDrive account and check that in wallet folder you have a file with .db extension.
9.- if everything it’s ok, now you can reinstall wallet full (remove and install) and perform a restore of your data (please wait until version 126.96.36.199 that I will be available during today).
Please when performing restore and backup, plugin into power and using wifi network, and always wait until it finished to avoid problems..