Fix ASN1 0X8009310A Bad Real Value Error

Yeah, that 0X8009310A error is a pain in the neck. I've seen it pop up on Windows 10 and Server 2016/2019 machines, usually when you're trying to install a driver, update software, or sometimes even run Windows Update. It's cryptic as hell, but the fix is usually straightforward. Let's get you unblocked.

The Quick Fix: Clear and Rebuild the Certificate Store

Press Win + R, type certmgr.msc, and hit Enter.
Expand Personal > Certificates.
If you see any certificates with a red or yellow icon (expired or invalid), right-click and delete them. But honestly, the real fix is to nuke the entire store and let it rebuild.
Close the certificate manager.
Open Command Prompt as Administrator (right-click Start, choose Command Prompt (Admin) or PowerShell (Admin)).
Run this command to stop the certificate propagation service:
```
net stop certpropagation
```

Now delete the machine-level certificate store:

del /q C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys\*

Restart the service:
```
net start certpropagation
```
Reboot your machine.

After reboot, Windows will rebuild the certificate store from scratch. Try whatever you were doing again. For most people, that clears the 0X8009310A error.

Why This Works

If you dig into the ASN.1 spec, 0X8009310A translates to a "bad real value" — meaning the certificate data is malformed or got corrupted. When Windows tries to read a cert file that's been half-written or damaged during an update or a bad third-party install, it throws this ASN.1 error. Deleting the MachineKeys folder forces Windows to recreate the local machine certificate store from the trusted root cache. It's like clearing a corrupted cache, and it solves the root cause instead of just suppressing the symptom.

Less Common Variations

Sometimes the error isn't in the machine store at all. I've seen cases where a specific application keeps its own certificate store and that's what's corrupt. Adobe products, Java runtime, even some custom line-of-business apps. For those:

Java: Run keytool -list to check the default cacerts. If you get errors, reimport the certs from a known good backup. Or just delete the cacerts file and copy from a fresh JDK install.
Adobe Reader: Reset its trust settings. Go to Edit > Preferences > Signatures > Identities & Trusted Certificates and clear the trust store.
Windows Update: If the error happens during Windows Update, run wuauclt.exe /updatenow after clearing the store, but also check the SoftwareDistribution folder — sometimes leftover download fragments cause this. Delete the contents of C:\Windows\SoftwareDistribution\Download.

Another variation: the error might be tied to a specific user profile's certificate store, not the machine store. If you've tried the machine fix and it's still failing when you're logged in as a particular user, try this:

certutil -user -store My

That lists the user's personal store. If you see corrupt entries, use certutil -delstore My "Certificate Number" to remove them. Replace "Certificate Number" with the actual serial from the output.

Last one: I had a client whose antivirus was interfering. Trend Micro and some suites with certificate pinning can trigger this error during installation of new software. Temporarily disable the AV's web protection, run your install, then re-enable. Took me two hours to figure that one out.

Prevention

Now how to stop this from happening again.

Don't randomly delete certificates from the Windows store. I see people cleaning up certificates with third-party tools, and they end up nuking vital ones. If you must clean, only remove ones that are clearly expired or that you know are invalid.
Keep Windows and your software updated. Microsoft has patched certificate handling bugs over the years. Outdated systems are more prone to this corruption.
Watch out for beta or unsigned drivers. Beta drivers often use test certificates that can corrupt the store when they expire. Stick to signed releases.
Backup your certificate store periodically. Open certmgr.msc, right-click the store you care about, choose All Tasks > Export, and save a .pfx file. If you ever get the error again, you can import it back instead of letting Windows rebuild from scratch — which sometimes loses custom certs.
If you're in a corporate environment, make sure Group Policy isn't pushing broken certs. Run gpupdate /force and check Event Viewer for CertificateServices errors. I've seen misconfigured autoenrollment trigger this exact error.

This error is annoying, but it's rarely a harbinger of doom. Clear the store, rebuild, and you're back in business. If you've tried all this and it's still failing, then we're talking about a deeper system corruption — but that's the exception, not the rule. I'd bet money the MachineKeys fix solves it for you.