So it looks like windows store and wallet have a pin. It seems that they forgot to give you a method to reset this pin. Is there a way to reset it? I can't find anything on the Microsoft account pages. And there seems to be no info mentioning a reset on the wallet FAQ
Microsoft brilliantly decided that the only way to solve this is to do a full reset on the phone. Make sure you manually sync before doing this if you've made changes recently. The re-sync process wasn't too bad, except that it takes a couple hours and then there are some system settings and other things like apps not remembering your account info. So it takes a while to fully 'restore' your phone.
You can see your Wallet pin from a computer that your logged on to with the same Microsoft Account: Go to Control Panel -> User Accounts -> Credential Manager, and chose Web Credentials. (this is how it works for me on Windows 10, if the version of Windows that your using doesn't follow this path, just type "Credential Manager" into the search on "Start"). Then scroll down to WalletPin and expand it (click the arrow next to it), then click "Show", you'll have to put your Microsoft Account password in. It should show you your Wallet Pin.