0x80040154 — Registering the server as an application failed / class not registered The COM class that opens this file type is not registered.
Work through these in order
- Re-register the owning application
- Check the bitness of the COM server
- Re-run the application’s registration step
One thing to keep in mind
Re-register after every major application upgrade.
Checked 2026-10-05 — R. Okonkwo.
Before changing anything
The code above is what an application reports; it is not a diagnosis of what went wrong. Two checks are worth doing before permissions are touched: whether the file is on a volume the application can actually reach, and whether the file was moved or renamed since it was last opened. Both report as this code more often than a permission problem does.
Pages in this section describe the code as applications report it. Where a fix is listed here, it is one the library has seen work on a real file; where nothing has been confirmed, the page says so instead of guessing at a cause.