FSX Deluxe + Acceleration on Windows 11: activation window won’t appear (missing MSXML4)

Roy,

You don’t want to go hunting random DLL downloads for this. Apart from the security risk, it usually doesn’t actually fix FSX activation on modern Windows because the activation UI relies on more than just one file.

Also, small but important correction: the file is msxml4.dll (Microsoft XML Core Services 4.0), not “msxmi4.dll”.

What I’d try first (safe + usually works)

1. Make sure FSX Deluxe (base) is fully installed and started once before touching Acceleration.
2. Right-click setup.exe on the FSX/Acceleration discs and choose Run as administrator.
3. Temporarily disable any “Controlled folder access” / ransomware protection in Windows Security (that feature can block the licensing/activation components from launching properly), then try the activation again.
4. Install outside Program Files if you can (example: C:\FSX\) to avoid UAC/file-virtualization weirdness.

MSXML4 specifically
Acceleration did commonly install prerequisites, but Windows 11 won’t always accept older bundled installers the same way Windows 7/8 did. The correct fix is to install MSXML 4.0 from Microsoft’s installer package, not to manually drop in a DLL from some site.

If you already have MSXML4 on the machine and it’s just not registering correctly, the only “manual” step I’d consider is re-registering the existing DLL (again: only if it’s already present on your system, not downloaded from a random place).

A few targeted questions so we don’t chase the wrong thing

• Is this the original boxed/DVD FSX Deluxe + Acceleration, or Steam Edition?
• Does the base FSX Deluxe activate/launch fine, and only Acceleration won’t activate? Or does neither activation window appear?
• When you try to activate, do you get any error message at all (even a brief popup), or does it simply do nothing?
• Where did you install FSX to (full path), and are you running the installer as admin?

Answer those and I can steer you to the cleanest fix for your exact case (there are a couple different failure modes on Windows 11, and they look similar from the outside).