Step 1: Repair Registry Entries Associated with Error 0x6D9

Manually editing the Windows registry to remove invalid Error 0x6D9 keys is not recommended unless you are PC service professional. Incorrectly editing your registry can stop your PC from functioning and create irreversible damage to your operating system. In fact, one misplaced comma can prevent your PC from booting entirely!

Because of this risk, we highly recommend using a trusted registry cleaner such as WinThruster [download] (Developed by Microsoft Gold Certified Partner) to scan and repair any Error 0x6D9-related registry problems. Using a registry cleaner [download] automates the process of finding invalid registry entries, missing file references (like the one causing your 0x6D9 error), and broken links within the registry. A backup is automatically created before each scan, with the ability to undo any changes in a single click, protecting you against the possibility of PC damage. The best part is that repairing registry errors [download] can also dramatically improve system speed and performance.

To manually repair your Windows registry, first you need to create a backup by exporting a portion of the registry related to Error 0x6D9 (eg. Windows Defender):

1. Click the Start button.
2. Type 'command' in the search box.. DO NOT hit ENTER yet!
3. While holding CTRL-Shift on your keyboard, hit ENTER.
4. You will be prompted with a permission dialog box.
5. Click Yes.
6. A black box will open with a blinking cursor.
7. Type 'regedit' and hit ENTER.
8. In the Registry Editor, select the Error 0x6D9-related key (eg. Windows Defender) you want to back up.
9. From the File menu, choose Export.
10. In the Save In list, select the folder where you want to save the Windows Defender backup key.
11. In the File Name box, type a name for your backup file, such as 'Windows Defender Backup'.
12. In the Export Range box, be sure that 'Selected branch' is selected.
13. Click Save.
14. The file is then saved with a .reg file extension.
15. You now have a backup of your Windows Defender-related registry entry.

The next steps in manually editing your registry will not be discussed in this article due to the high risk of damaging your system. If you would like to learn more about manual registry editing, please see the links below.

Windows XP
http://www.theeldergeek.com/windows_xp_registry.htm

Windows 7
http://www.theeldergeek.com/windows_7/registry_edits_for_win7.htm

Windows Vista
http://support.microsoft.com/kb/2688326 - LetMeFixItMyselfAlways

Step 2: Conduct a Full Malware Scan of Your PC

There is a chance that your 0x6D9 error could be related to a malware infection on your PC. These malicious intruders can damage, corrupt, or even delete Runtime Errors-related files. Furthermore, there's a possibility that the 0x6D9 error you are experiencing is related to a component of the malicious program itself.

Step 3: Clean Out Your System Junk (Temporary Files and Folders) With Disk Cleanup (cleanmgr)

Over time, your computer accumulates junk files from normal web surfing and computer use. If this junk isn't occasionally cleaned out, it can cause Windows Defender to respond slowly or provides an 0x6D9 error, possibly due to file conflicts or an overloaded hard drive. Cleaning up these temporary files with Disk Cleanup might not only solve your 0x6D9 error, but can also dramatically speed up the performance of your PC.

Because of the shortcomings of the Windows Disk Cleanup (cleanmgr) tool, we highly recommend using a specialized hard drive cleanup / privacy protection software such as WinSweeper [download] (Developed by Microsoft Gold Partner) to clean up your entire computer. Running WinSweeper [download] once per day (using automatic scanning) will ensure that your computer is always clean, running fast, and free of 0x6D9 errors related to temporary files.

How to run Disk Cleanup (cleanmgr) (Windows XP, Vista, 7, 8, and 10):

1. Click the Start button.
2. Type 'command' in the search box.. DO NOT hit ENTER yet!
3. While holding CTRL-Shift on your keyboard, hit ENTER.
4. You will be prompted with a permission dialog box.
5. Click Yes.
6. A black box will open with a blinking cursor.
7. Type 'cleanmgr' and hit ENTER.
8. Disk Cleanup will begin calculating how much occupied disk space you can reclaim.
9. The Disk Cleanup dialog box will appear with series of checkboxes you can select. In most cases, the 'Temporary Files' category will occupy the most disk space.
10. Check the boxes of the categories you want to clean and click OK.

Step 4: Update Your PC Device Drivers

0x6D9 errors can be related to corrupt or outdated device drivers. Drivers can work one day, and suddenly stop working the next day, for a variety of reasons. The good news is that you can often update the device driver to fix the Error 0x6D9 problem.

Finding the exact driver for your Error 0x6D9-related hardware device can be extremely difficult, even directly on the Microsoft Corporation or related manufacturer's website. Even if you are experienced at finding, downloading, and manually updating drivers, the process can still be very time consuming and extremely irritating. Installing the wrong driver, or simply an incompatible version of the right driver, can make your problems even worse.

Because of the time and complexity involved in updating drivers, we highly recommend using a driver update tool such as DriverDoc (Developed by Microsoft Gold Partner) to automate the process.

DriverDoc updates all of your PC device drivers, not just those associated with your 0x6D9 error. DriverDoc's proprietary One-Click Update™ technology not only ensures that you have correct driver versions for your hardware, but it also creates a backup of your current drivers before making any changes. Maintaining a driver backup provides you with the security of knowing that you can rollback any driver to a previous version if necessary. With updated device drivers, you can finally unlock new hardware features and improve the speed and performance of your PC.

Step 5: Utilize Windows System Restore to 'Undo' Recent System Changes

Windows System Restore allows you to 'go back in time' with your PC to help fix your Error 0x6D9 problems. System Restore can return your PC's system files and programs back to a time when everything was working fine. This can potentially help you avoid hours of troubleshooting headaches associated with 0x6D9 errors.

To use System Restore (Windows XP, Vista, 7, 8, and 10):

1. Click the Start button.
2. In the search box, type 'System Restore' and hit ENTER.
3. In the results, click System Restore.
4. Enter any administrator passwords (if prompted).
5. Follow the steps in the Wizard to choose a restore point.
6. Restore your computer.

Step 6: Uninstall and Reinstall the Windows Defender Program Associated with Error 0x6D9

If your 0x6D9 error is related to a specific program, reinstalling Windows Defender-related software could be the answer.

Instructions for Windows 7 and Windows Vista:

1. Open Programs and Features by clicking the Start button.
2. Click Control Panel on the right side menu.
3. Click Programs.
4. Click Programs and Features.
5. Locate Windows Defender Error Code 0X6D9-associated program (eg. Windows Defender) under the Name column.
6. Click on the Windows Defender-associated entry.
7. Click the Uninstall button on the top menu ribbon.
8. Follow the on-screen directions to complete the uninstallation of your Error 0x6D9-associated program.

Instructions for Windows XP:

1. Open Programs and Features by clicking the Start button.
2. Click Control Panel.
3. Click Add or Remove Programs.
4. Locate Windows Defender Error Code 0X6D9-associated program (eg. Windows Defender) under the list of Currently Installed Programs.
5. Click on the Windows Defender-associated entry.
6. Click the Remove button on the right side.
7. Follow the on-screen directions to complete the uninstallation of your Error 0x6D9-associated program.

Instructions for Windows 8:

1. Hover the cursor in the bottom left of the screen to produce the Start Menu image.
2. Right-Click to bring up the Start Context Menu.
3. Click Programs and Features.
4. Locate Windows Defender Error Code 0X6D9-associated program (eg. Windows Defender) under the Name column.
5. Click on the Windows Defender-associated entry.
6. Click the Uninstall/Change on the top menu ribbon.
7. Follow the on-screen directions to complete the uninstallation of your Error 0x6D9-associated program.

After you have successfully uninstalled your Error 0x6D9-associated program (eg. Windows Defender), reinstall the program according to the Microsoft Corporation instructions.

Step 7: Run Windows System File Checker ('sfc /scannow')

System File Checker is a handy tool included with Windows that allows you scan for and restore corruptions in Windows system files (including those related to Error 0x6D9).

To run System File Checker (Windows XP, Vista, 7, 8, and 10):

1. Click the Start button.
2. Type 'command' in the search box.. DO NOT hit ENTER yet!
3. While holding CTRL-Shift on your keyboard, hit ENTER.
4. You will be prompted with a permission dialog box.
5. Click Yes.
6. A black box will open with a blinking cursor.
7. Type 'sfc /scannow' and hit ENTER.
8. System File Checker will begin scanning for Error 0x6D9 and other system file problems (be patient - the system scan may take a while).
9. Follow the on-screen commands.

Step 8: Install All Available Windows Updates

Microsoft is constantly updating and improving Windows system files that could be associated with Error 0x6D9. Sometimes resolving your Runtime Errors problems may be as simple as updating Windows with the latest Service Pack or other patch that Microsoft releases on an ongoing basis.

To check for Windows Updates (Windows XP, Vista, 7, 8, and 10):

1. Click the Start button.
2. Type 'update' into the search box and hit ENTER.
3. The Windows Update dialog box will appear.
4. If updates are available, click the Install Updates button.

Step 9: Perform a Clean Installation of Windows

This step is your final option in trying to resolve your Error 0x6D9 issue. Reinstalling Windows will erase everything from your hard drive, allowing you to start again with a fresh system. Furthermore, a clean install of Windows will also quickly clean out any and all 'junk' that has accumulated over the normal usage of your computer.