0x80040154
Class not registered
What it means
Outlook tried to create a component that is not registered on this PC, often after a broken Office update.
Common causes
- A damaged Office installation
- A third-party add-in that failed to register
- A 32/64-bit mismatch
How to fix it
- Start Outlook in safe mode:
outlook.exe /safe. - Disable add-ins one at a time under File > Options > Add-ins.
- Repair Office from Settings > Apps > Microsoft 365 > Modify > Quick Repair, then Online Repair.
- Reinstall Office if the component is still missing.