ERROR: 'Unable to cast COM object of type... Interface not registered ...'

Solution Properties

Solution ID:

260624105620293

Last Modified Date:

Wed Jun 24 11:30:08 UTC 2026

Taxonomy Path:

Case category//I have a problem with...//email

Author:

[email protected]

ERROR: 'Unable to cast COM object of type... Interface not registered ...'

Description

When you try to send emails from your software using Outlook, you can see the error:

'Unable to send all emails. Error with the address. Unknown Error. Check Windows event Log for more details.'

When you check your Windows Event Log, you'll see:

Error: 'Unable to cast COM object of type Microsoft.Office.Interop.Outlook.ApplicationClass' to interface type 'Microsoft.Office.Interop.Outlook._Application'. This operation failed because the QueryInterface call on the COM component for the interface with IID '...failed due to the following error: Interface not registered...'

The full Unable to case COM object error message.

NOTE:

If you see a different error, use our event log errors when sending emails with Microsoft Outlook or SMTP article.

Cause

Resolution

Repair your Outlook installation

An issue with the Outlook installation causes this error. For example, after downgrading Outlook.

Run a repair of the Outlook installation, then check you've resolved the issue. For help with doing this, or for further troubleshooting, contact your IT support.

[BCB:19:UK - Sales message :ECB]

Steps to duplicate