How do I fix the MSXML 4.0 error in Flight Simulator X (FSX)?
The FSX MSXML 4.0 error usually means the old XML component that boxed Flight Simulator X expects is missing, damaged or no longer registered in Windows. The usual fix is to remove the broken MSXML 4.0 entry, reinstall or repair it from your original FSX media, then repair FSX or the add-on that triggered the error.
What causes the MSXML 4.0 error in FSX?
FSX is an older 32-bit simulator, and the original boxed release relies on legacy Microsoft components during installation and, in some cases, at launch. One of those is MSXML 4.0. If that component is incomplete, corrupted, or replaced by a bad add-on installer, FSX can fail with an MSXML message.
We most often see it in three situations:
- During FSX installation when setup cannot install or detect MSXML 4.0 correctly.
- When starting FSX if the MSXML file is present but not properly registered in Windows.
- After installing an older add-on that brought its own legacy files or altered shared components.
Are you using boxed FSX or FSX: Steam Edition?
This matters. Boxed FSX is far more likely to throw an MSXML 4.0 error. FSX: Steam Edition generally handles prerequisites more cleanly, so if you see this there, an older add-on is often the real cause.
| Version | How common is the error? | Most likely cause |
|---|---|---|
| Boxed FSX | Common enough on modern Windows | Missing or broken legacy prerequisite during install or launch |
| FSX: Steam Edition | Less common | Older add-on installer or damaged shared XML component |
How do we fix the MSXML 4.0 error in FSX?
- Confirm where the error appears
Note whether the message appears during FSX installation, when launching the simulator, or only after installing an add-on. That tells us whether we should repair the base simulator, the XML component itself, or the add-on that likely caused it.
- Close FSX and any installer windows
Shut down FSX fully before changing anything. If an installer is stuck, close it and restart Windows so you are not repairing files while another setup program still has them in use.
- Check whether MSXML 4.0 is already installed
Open the Windows list of installed apps and look for an MSXML 4.0 entry. If you find one, try a repair first if Windows offers that option. If not, uninstall that entry so you can reinstall a clean copy from your own FSX files.
If uninstall fails, do not force random fixes from DLL download sites. That often makes FSX harder to repair later.
- Restart Windows
Reboot before reinstalling MSXML 4.0. Old shared components can remain locked in memory, and a restart clears that state.
- Reinstall MSXML 4.0 from your original FSX media
Use the prerequisite installer included with your boxed FSX discs or original installer package. Run it as an administrator. We strongly recommend using only the Microsoft-supplied copy that came with your simulator or add-on media, not a loose file from an unknown source.
If you are on FSX: Steam Edition, this step usually only applies when an older add-on specifically expects MSXML 4.0. In that case, repair the component first, then reinstall the add-on.
- Register the MSXML 4.0 DLL manually if the error still appears at launch
Sometimes the file is present but Windows has lost the registration. Open an elevated Command Prompt and register the 32-bit DLL that FSX uses.
On 64-bit Windows, the command is usually
regsvr32 C:\Windows\SysWOW64\msxml4.dll.On 32-bit Windows, it is usually
regsvr32 C:\Windows\System32\msxml4.dll.If registration succeeds, restart Windows and test FSX again. If Windows says the file cannot be found, that points back to a missing or incomplete MSXML installation.
- Repair or reinstall FSX
If the XML component is now installed correctly but FSX still errors, repair the simulator from its original installer. If the original install never completed properly, a clean uninstall and reinstall is often faster than trying to patch a half-installed copy.
For boxed FSX, install the base simulator first, then any official acceleration or service content you already own, then your add-ons. Do not pile everything back in at once until the base sim launches cleanly.
- Reinstall the add-on that triggered the issue
If the problem started right after one particular aircraft, scenery or utility, reinstall that add-on only after FSX opens normally again. Older installers can leave broken shared files behind, so fixing the base component first matters.
What if the error happens during FSX installation?
If setup stops with an MSXML 4.0 message before FSX finishes installing, the cleanest route is usually this:
- Remove the failed FSX installation
Uninstall any partial FSX install from Windows if it appears there.
- Remove or repair the existing MSXML 4.0 entry
If Windows lists MSXML 4.0, repair it or uninstall it.
- Restart the PC
This clears locked installer files and pending changes.
- Run the prerequisite installer first
Install the MSXML 4.0 component from your FSX media before launching the main FSX setup.
- Run FSX setup as administrator
That avoids permissions issues that are common on newer versions of Windows.
This order solves a lot of stubborn boxed-FSX installs on Windows 10 and Windows 11.
What if Windows will not uninstall MSXML 4.0?
That usually means the existing install is damaged. In practice, we try a repair first, then a restart, then a reinstall from the original media. If Windows still refuses to remove it, the next sensible move is a full FSX reinstall after clearing the failed setup, rather than layering more fixes on top of a broken shared component.
The important part is not to start dropping individual XML DLL files into random folders. FSX depends on proper Windows registration, not just the presence of a file.
Should I download msxml4.dll from a DLL site?
No. We do not recommend that at all. Those files are frequently the wrong version, unregistered, or bundled in unsafe downloads. Even if FSX starts once, you can end up with a less stable system and harder-to-diagnose add-on issues later.
Use the Microsoft-supplied installer from your own FSX media or from the original add-on package that legitimately included it.
Common MSXML 4.0 symptoms and the best fix
| Symptom | Likely cause | Best fix |
|---|---|---|
| FSX setup stops with an MSXML 4.0 error | Broken or missing prerequisite | Repair or remove MSXML 4.0, restart, install the prerequisite first, then rerun FSX setup |
| FSX launches, then shows an MSXML message | DLL present but not registered, or damaged | Reinstall MSXML 4.0 and register msxml4.dll |
| Error started after adding an aircraft or utility | Older add-on altered shared files | Repair MSXML 4.0, then reinstall the affected add-on |
| FSX: Steam Edition shows the error | Usually add-on related, not the base sim | Repair the component and check the add-on's Steam compatibility |
If the problem keeps coming back
If you fix MSXML 4.0 and the error returns after installing the same older add-on, the add-on installer is probably the root cause. At that point, look for an updated FSX or FSX: Steam Edition version of that product, or leave it out of the build.
Also keep your FSX installation disciplined. Install the simulator, confirm it runs, then add one aircraft or scenery package at a time. That makes it much easier to spot which installer broke the XML component.
The short version
For most users, the reliable fix is simple: remove or repair the broken MSXML 4.0 installation, reinstall it from the original FSX media, register msxml4.dll if needed, then repair or reinstall FSX. If you are on FSX: Steam Edition, suspect an older add-on first rather than the simulator itself.