How to Fix 'Class not registered (Exception from HRESULT: 0x80040154 (REGDB_E_CLASSNOTREG))' COM Errors?

Fixing the "Class Not Registered" COM Exception (REGDB_E_CLASSNOTREG)

This guide addresses the common COM error, "Class not registered (Exception from HRESULT: 0x80040154 (REGDB_E_CLASSNOTREG))", which occurs when creating a COM class instance. The root cause is usually an improperly registered COM component in the Windows registry.

Solutions:

Here's a breakdown of troubleshooting steps:

1. Confirm Build Architecture: Double-check that your project's build architecture matches your runtime environment. If you're running a 64-bit system, ensure your assemblies are compiled for x64. If the error persists in a 64-bit environment, try switching to an x86 (32-bit) build configuration.

2. Reinstall the COM Component: If the architecture isn't the problem, reinstalling the COM component is the next step. Carefully follow the installation instructions, paying close attention to the registry registration aspect of the installation.

3. Manual Registry Registration: Use the regsvr32 command-line tool to manually register the COM component. Open an elevated Command Prompt (run as administrator) and execute:

<code>regsvr32 "<path_to_com_dll>"</code>

Remember to replace <path_to_com_dll> with the complete path to your COM DLL.

4. Dependency Check: Use a dependency analysis tool like Dependency Walker to identify any missing dependencies for your COM component. Ensure all required assemblies are correctly registered.

5. Permissions and Server Configuration: Verify that the user account running the code has the necessary permissions to access the COM server. Also, review your COM server configuration, checking firewall rules and network settings for any potential restrictions.

By systematically applying these solutions, you should be able to resolve the "Class not registered" error and successfully instantiate your COM class.

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