FS9.1 won’t start on Windows 11 due to missing installation security certificate

Henrik,

That “security certificate / publisher field is empty” message is almost always Windows blocking an older installer/exe because it’s unsigned (or the signature can’t be validated anymore), not because Microsoft is “deleting” anything during install. FS2004 (9.1) predates modern Windows trust/signing expectations, and Windows 11 can be a lot less forgiving when something tries to run from a protected location or with legacy compatibility flags.

Here’s what I’d try, in order.

1) Don’t install (or run) it from Program Files
If FS9 is under:
C:\Program Files\
or
C:\Program Files (x86)\
move away from there. The easiest “known good” path is something like:
C:\FS9\

If it’s already installed under Program Files, I’d honestly uninstall and reinstall to a simple folder like above (copying the folder after the fact can work, but it often leaves registry/app paths pointing to the old location).

2) Run the EXE with compatibility + admin (just for first launch)
Go to your FS9 folder, right-click:
fs9.exe
then:

1. Properties
2. Compatibility tab
3. Check “Run this program in compatibility mode” and pick Windows XP (Service Pack 3) (or Windows 7 if XP isn’t available)
4. Check “Run this program as an administrator”
5. Apply / OK

Then launch it once directly from fs9.exe (not a Start Menu shortcut).

3) Make sure Windows Security isn’t silently blocking it
Windows 11 will sometimes block older EXEs with SmartScreen / reputation protection and the symptom can look like a certificate/publisher issue.

Please check:

• Windows Security
• App & browser control
• Reputation-based protection (and any recent blocks in Protection history)

If there’s an entry for FS9 being blocked, allow it (or temporarily disable reputation-based blocking just long enough to confirm that’s the cause, then re-enable it).

4) Confirm you’re launching the patched EXE
If you have multiple FS9 folders, it’s easy to be clicking an old shortcut pointing to the wrong one. Make sure the shortcut points to the actual:
...\fs9.exe
in the folder you think you’re using.

A couple of targeted questions so I don’t send you down the wrong path

1. Are you trying to start the FS9.1 update installer, or are you trying to start the sim itself ( fs9.exe) after patching?
2. Where is FS9 installed right now (exact folder path)?
3. What exact Windows message are you seeing (a screenshot is fine), and is it coming from SmartScreen, Windows Installer, or a properties “Digital Signatures” tab?
4. Is this the CD/DVD version, or a downloaded installer (and if downloaded, from where)?

Answer those and I can narrow it down quickly—FS9 can run on Windows 11, but you usually have to be careful about install location and Windows Security getting in the way.