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This guide is provided by Conductor, the service that powers the QuickBooks Desktop integration for many business tools, including the one that sent you here.
If a Conductor error message directed you to this page, it’s because we encountered the following error when attempting to connect to QuickBooks Desktop on your computer: 
Unable to cast COM object of type 'System.__ComObject' to interface type
'Interop.QBXMLRP2.RequestProcessor2'. This operation failed because the
QueryInterface call on the COM component for the interface with IID
'{8DB91B17-D5A2-41DB-80A7-CC6F1E449A05}' failed due to the following error:
No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

​
Solution

Complete the following steps to re-register the QuickBooks Desktop components to resolve this issue:
1

Close QuickBooks Desktop

Ensure QuickBooks Desktop is completely closed.
2

Open Command Prompt (cmd.exe) as an administrator

Using Windows search (usually located in the bottom-left corner of your screen), type “cmd”, right-click on the “Command Prompt” result, and select “Run as administrator”.Run Command Prompt as administrator
3

Run the command to re-register QuickBooks components

Copy the entire command below, then paste it into the PowerShell window and press Enter.
"%windir%\SysWOW64\regsvr32.exe" "C:\Program Files (x86)\Common Files\Intuit\QuickBooks\QBXMLRP2.dll"
Re-register QuickBooks components via Command PromptIf the command was successful, you will see a success message resembling the screenshot below.Re-register QuickBooks components via Command Prompt
4

Restart your computer

If the command was successful, restart your computer to ensure the changes take effect. After restarting, try connecting to QuickBooks Desktop again.
These steps should resolve the COM object casting error by properly registering the QuickBooks components with your system.