Hi Karl,
That problem usually shows up if one of these 3 things is true:
1. No internet connection - MSFS needs to verify connection back to store at startup
2. Windows Time & Language settings are wonky. The game must see your current location and time zone that matches the account you made the purchase with
3. Anti virus has suddenly quarantined your executable.....if so, and you determine it was an error, you can exclude the executable from windows security
Rod