Unable to cast COM object of type System.__ComObject to IRibbonUI. IID 00c03a7-0000-0000-c000-000000000046 TYPE_E_LIBNOTREGISTERED 0x8002801d

After applying Microsoft .NET patches or upgrade and then subsequent downgrade of Microsoft Office, I am getting an error:

Unable to cast COM object of type System.__ComObject to IRibbonUI. IID 00c03a7-0000-0000-c000-000000000046 Library not registered TYPE_E_LIBNOTREGISTERED 0x8002801d

in an error window of Invantive Control when starting Microsoft Excel 2010.

A similar error occurs when installing Skype for Business with Office 2010:

Microsoft.Office.Core.IRibbonUI'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{000C03A7-0000-0000-C000-000000000046}' failed due to the following error: Library not registered. (Exception from HRESULT: 0x8002801D (TYPE_E_LIBNOTREGISTERED)).'

How can I fix this?

The problem seems to occur only when Office 2010 is involved; the problem has never been seen on Office 2013 or 2016.

It seems that Microsoft installers replace registrations, but don't cover all components especially with a downgrade back.

The recommended steps are:

• Make sure you have a tested backup of the device and registry so you can return to the original situation.
• Re-install the correct version of Visual Studio Tools for Office, such as from Visual Studio Tools for Office 2010.
• Re-install Invantive Control from Invantive Control site.
• Check whether the problem is resolved. If not, things get more tricky:
• Take the GUID from the eror message ({000C03A7-0000-0000-C000-000000000046}).
• Open registry editor in elevated mode.
• Find the GUID {000C03A7-0000-0000-C000-000000000046}.
• Go to the TypeLib node.
• Copy the GUID from there ({2DF8D04C-5BFA-101B-BDE5-00AA0044DE52}).
• Find {2DF8D04C-5BFA-101B-BDE5-00AA0044DE52}.
• It lists multiple version numbers.
• Make sure you have a tested backup of the registry.
• Remove the 2.8 version number, keeping the 2.5 version.
• Restart Excel.
• When this doesn't help, the most easy route is to re-install Windows or test with Excel 2013 or 2016.