>> "What has changed? "
Nothing, the folder you gave "all user permissions" to might have changed when you upgraded the PC. Or whatever Installer you're using doesn't correctly set the permissions.
If you want wyUpdate to never prompt for admin permissions then you need to ensure you never write the non-user registry, and that you install your app in a user controlled folder (%appdata%, document, desktop, etc.) OR write to a "system" folder that has given read/write/delete permission (and "ownership" permissions) to *all* users.
Or, just install your app normally in a system folder and have wyUpdate work as-designed and ask for permissions before updating your app.
>> "We also note that the code signing certificates on your wyUpdate expired last year. Please release a new version."
A new version is coming soon. An no, the signing has not expired (they're time-stamp signed, meaning even if the cert expires the signature is still valid).