What is Microsoft Core XML Services 6.0 / 4.0 SP3?

Microsoft XML Core Services (MSXML) 6.0 and 4.0 SP3 errors typically occur when older software or classic PC games (like Age of Empires III) cannot locate or register the required msxml4.dll or msxml6.dll files on modern versions of Windows. Because MSXML 4.0 reached End-of-Life (EOL) years ago, modern Windows operating systems do not include it by default, causing installation and runtime failures. Common Error Symptoms

“MSXML 4.0 is not installed correctly” during legacy game or software launches.

“An error occurred during the installation of assembly component” (such as error code 0x80070422) during manual setup.

Windows Update loops, where the system continuously prompts you to install security updates like KB2758694. Step-by-Step Fixes 1. Manually Re-register the MSXML DLLs

If the files exist but your software cannot see them, forcing Windows to re-index the component often solves the problem immediately.

Open Command Prompt as Administrator: Click Start, type cmd, right-click it, and select Run as Administrator.

Navigate to the system folder: Type cd \windows\syswow64 (for 64-bit systems) or cd \windows\system32 (for 32-bit systems) and press Enter.

Register MSXML 6.0: Type regsvr32 msxml6.dll and press Enter.

Register MSXML 4.0: Type regsvr32 msxml4.dll and press Enter.

2. Run the Installer in Compatibility Mode (For MSXML 4.0 SP3)

Because MSXML 4.0 SP3 was designed for Windows XP and Windows 7, modern Windows ⁄₁₁ installers block it due to OS incompatibility.