| Previous | Next |
| WPN_E_NOTIFICATION_ID_MATCHED | WPN_E_TOAST_NOTIFICATION_DROPPED |
WPN_E_CALLBACK_ALREADY_REGISTERED
WPN_E_CALLBACK_ALREADY_REGISTERED is an HRESULT used by the Windows notification platform. It means that code attempted to register a notification callback when the platform already has a callback registration for the same notification path.
What to check for WPN_E_CALLBACK_ALREADY_REGISTERED
- Register the callback once and share it across components that need notification events.
- Unregister or replace callbacks only through the documented lifecycle API.
- Protect registration with synchronization when startup and background activation can race.
Diagnostic discriminator: Inspect callback ownership before registering again. An existing registration for the same notification path distinguishes this lifecycle error from callback invocation failure or notification delivery problems.
Looking for a different code? Search another status or error code.