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).

Roy,

That helps a lot. Since base FSX activates and runs, we can stop chasing “general FSX on Win11” issues and focus specifically on the Acceleration activation component.

Also, you’re right that Microsoft doesn’t host MSXML 4.0 the way they used to. But I still would not try to “source” a loose msxml4.dll from anywhere. With MSXML4 you need a proper, registered install (and the activation error you posted is very commonly a registration/prereq issue, not just “missing DLL file”).

What I’d do next (in order)

1) Confirm whether MSXML4 is actually missing, or just not registering

1. Go to Windows “Apps” (Installed apps) and see if anything like “MSXML 4.0” / “MSXML 4.0 SP…” is listed.
2. Also check these folders for the file:
   C:\Windows\System32\msxml4.dll
C:\Windows\SysWOW64\msxml4.dll

If it’s in one/both places, you’re not “missing the DLL”, it’s more likely unregistered or broken.

2) If msxml4.dll exists, re-register it (safe check)
Open an elevated Command Prompt (Run as Administrator) and run:
regsvr32 C:\Windows\System32\msxml4.dll
regsvr32 C:\Windows\SysWOW64\msxml4.dll
You should get a “DllRegisterServer succeeded” message.

If you get “module not found”, “entry point not found”, or access denied, tell me the exact wording.

3) Re-run Acceleration’s activation trigger as admin
Even if you already “installed as admin”, the activation UI can be blocked by security/UAC at the moment it tries to launch.

1. Right-click the Acceleration setup.exe on the DVD and choose Run as administrator.
2. Temporarily turn OFF Windows Security “Controlled folder access” (if it’s enabled) just for this test, then run activation again.
3. Reboot once after any MSXML register attempt, then try the Acceleration start again.

4) Don’t worry about KB2758694 specifically yet
That “msxml4-KB2758694-enu.exe” file being absent from your DVD is not unusual depending on the disc run/printing. It’s a security update package, not the core runtime itself. The bigger question is simply: does your system have a working MSXML4 runtime registered.

A couple quick questions so I can point you to the cleanest “no sketchy DLLs” fix

• When you get the 0x800040005 error, where exactly does it show (Acceleration installer dialog, FSX splash screen, inside FSX when selecting Acceleration content, etc.)?
• After installing Acceleration, does FSX show “Microsoft Flight Simulator X: Acceleration” on the startup screen, or does it still look like plain FSX?
• Do you have “Controlled folder access” enabled right now (Windows Security -> Ransomware protection)?
• When you run the regsvr32 commands above, what exact message(s) do you get?

Once I know those four, I can tell you whether this is (a) a straightforward MSXML4 registration/prereq fix, or (b) the activation UI being blocked by Win11 security controls, which looks almost identical from the outside but needs a different approach.