Fix OSS_BAD_TIME (0X8009300C) Certificate Error in Windows

Quick answer for advanced users: Run w32tm /resync in an admin Command Prompt, then check your BIOS clock and time zone.

Why You're Seeing 0X8009300C

This error means OSS_BAD_TIME — the certificate thinks the time is wrong. It's not a certificate corruption issue. It's a clock problem. Your system's date and time don't match what the ASN certificate expects. This triggers the 0X8009300C error.

I've seen this happen after a motherboard battery dies, after daylight saving time changes, or when Windows time sync gets turned off. Once I helped a user who had changed their clock manually to test an app and forgot to set it back. That's all it takes.

Step-by-Step Fix

Check the date and time in the bottom-right corner of your screen. Right-click the clock and pick Adjust date/time. Turn on Set time automatically and Set time zone automatically.
Sync the clock with Windows Time service. Open Command Prompt as administrator (right-click Start and pick Command Prompt or Terminal Admin). Type:
```
w32tm /resync
```
If it says "The command completed successfully," your time is now correct. If it fails, move to the next step.
Restart the Windows Time service. In the same Command Prompt, run:
```
net stop w32time && net start w32time
```
Then run w32tm /resync again.
Check your BIOS clock. Restart your PC and press F2, Del, or Esc (depends on your motherboard) to enter BIOS/UEFI. Look for the date and time setting. Fix it if it's wrong. Then save and exit.
Update your time zone. Go back to Date & Time settings and make sure the time zone matches where you live. If you're in a region without daylight saving time, turn off "Adjust for daylight saving time automatically."

Alternative Fixes If the Main One Fails

Sometimes the automatic sync doesn't work because Windows can't reach the time server. Try these:

Use a different NTP server. In Date & Time settings, click Additional date, time & regional settings, then Set the time for other time zones. You can also set the server manually in the registry, but it's easier to use third-party tools like NetTime (free and lightweight).
Check for malware. Some malware messes with the system clock. Run a full scan with Windows Defender or your antivirus.
Replace the CMOS battery. If your clock resets every time you turn off the PC, the battery is dead. It's a coin-cell CR2032 battery inside your PC. Costs around $2. Swap it yourself — it's easy.

Prevention Tip

Keep automatic time sync on. That's it. If you travel a lot, set the time zone manually in Windows so it doesn't flip when you cross borders. Once I turned off time sync to save battery on a laptop and forgot about it. Three months later I hit this error. Learn from my mistake — leave it on.

When to Call a Professional

If you've done all this and still get 0X8009300C, the certificate itself might be corrupted, or there's a deeper issue with the certificate store. Try running certutil -repairstore my in an admin Command Prompt. If that doesn't work, you might need to reinstall the application that uses the certificate. That's rare though. 90% of the time it's just the clock.