How to Solve 'Class Not Registered' COM Exception (0x80040154)?

Resolving the "Class Not Registered" COM Exception

When instantiating a COM class, you might encounter the error:

<code>Class not registered (Exception from HRESULT: 0x80040154 (REGDB_E_CLASSNOTREG))</code>

This signifies that the COM class your code uses isn't correctly registered on your system. Here's how to fix it:

1. Architecture Alignment:

Confirm that all your assemblies are built for the correct system architecture. If the error occurs in a 64-bit environment, ensure your assemblies are compiled for x64. Rebuilding your solution for x86 might resolve the problem.

2. Re-register the COM Component:

If the architecture isn't the issue, try reinstalling the COM component referenced in your code. The installer or registry information for COM components is typically found within the Microsoft Visual Studio Tools for Office installer or the Windows registry (under HKCR\CLSID).

Helpful Techniques:

• Visual Studio's Registry Editor: Visual Studio includes a Registry Editor for examining and adjusting COM registration settings.
• Regasm.exe Utility: The Windows RegAsm utility allows manual registration and unregistration of COM classes.
• Enabling 32-bit Applications: In 64-bit environments, ensure 32-bit application support is enabled by setting the Enable32BitApplications registry key to 1 (located at HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows).

By following these steps, you can effectively diagnose and resolve COM registration exceptions, ensuring your application runs without interruption.

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