What are ntdef.chm Error Messages?

General ntdef.chm Runtime Errors

ntdef.chm file errors often occur during the startup phase of Windows, but can also occur while the program is running. These types CHM errors are also known as “runtime errors” because they occur while Windows is running. Here are some of the most common ntdef.chm runtime errors:

• ntdef.chm could not be found.
• ntdef.chm error.
• ntdef.chm failed to load.
• Error loading ntdef.chm.
• Failed to register ntdef.chm / Cannot register ntdef.chm.
• Runtime Error - ntdef.chm.
• The file ntdef.chm is missing or corrupt.

Most CHM errors are due to missing or corrupt files. Your ntdef.chm file could be missing due to accidental deletion, uninstalled as a shared file of another program (shared with Windows), or deleted by a malware infection. Furthermore, ntdef.chm file corruption could be caused from a power outage when loading Windows, system crash while loading or saving ntdef.chm, bad sectors on your storage media (usually your primary hard drive), or malware infection. Thus, it’s critical to make sure your anti-virus is kept up-to-date and scanning regularly.

How to Fix ntdef.chm Errors in 3 Steps (Time to complete: ~5-15 minutes)

If you're encountering one of the error messages above, follow these troubleshooting steps to resolve your ntdef.chm issue. These troubleshooting steps are listed in the recommended order of execution.

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

1. Hit the Windows Start button
2. When you see the search box, type "System Restore" and press "ENTER".
3. In the search results, find and click System Restore.
4. Please enter the administrator password (if applicable / prompted).
5. Follow the steps in the System Restore Wizard to choose a relevant restore point.
6. Restore your computer to that backup image.

If the Step 1 fails to resolve the ntdef.chm error, please proceed to the Step 2 below.

When the first two steps haven't solved your issue, it might be a good idea to run Windows Update. Many ntdef.chm error messages that are encountered can be contributed to an outdated Windows Operating System. To run Windows Update, please follow these easy steps:

1. Hit the Windows Start button
2. In the search box, type "Update" and press "ENTER".
3. In the Windows Update dialog box, click "Check for Updates" (or similar button depending on your Windows version)
4. If updates are available for download, click "Install Updates".
5. After the update is completed, restart your PC.

If Windows Update failed to resolve the ntdef.chm error message, please proceed to next step. Please note that this final step is recommended for advanced PC users only.

If Those Steps Fail: Download and Replace Your ntdef.chm File (Caution: Advanced)

If none of the previous three troubleshooting steps have resolved your issue, you can try a more aggressive approach (Note: Not recommended for amateur PC users) by downloading and replacing your appropriate ntdef.chm file version. We maintain a comprehensive database of 100% malware-free ntdef.chm files for every applicable version of Windows. Please follow the steps below to download and properly replace you file:

1. Locate your Windows operating system version in the list of below "Download ntdef.chm Files".
2. Click the appropriate "Download Now" button and download your Windows file version.
3. Copy the file into the appropriate directory for your Windows version:


Windows XP: C:\WINDOWS\Help\

4. Restart your computer.

If this final step has failed and you're still encountering the error, you're only remaining option is to do a clean installation of Windows XP.

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