Can’t read .chm (Compiled Help) on Vista/XP/2003?

In my previous post, I mentioned that TechNet Magazine has their past issues available in HTML Help format (.chm) here.  If you navigate to that page (with a fully patched Vista or Windows XP box) and open one of the referenced files from directly within IE, you will get something that looks a bit like the following: "The address is not valid".

The reason for this problem is addressed in the following KB article: You cannot open HTML Help files from Internet Explorer after you install security update 896358 or Windows Server 2003 Service Pack 1


After you install security update 896358 or Microsoft Windows Server 2003 Service Pack 1 (SP1), you may experience one or both of the following symptoms after you click a link to an HTML Help .chm file in Internet Explorer:

  • Topics in the .chm file cannot be viewed when you click Open instead of Save in the File Download dialog box.
  • Topics in the .chm file cannot be viewed when you click Save in the File Download dialog box, and you then try to open the file.


Security update 896358 and Windows Server 2003 SP1 include changes to the InfoTech protocol that block the ability to view remote content. These changes were introduced to reduce security vulnerabilities in HTML Help. After you install 896358 or Windows Server 2003 SP1, files in the Temporary Internet Files folder are treated as content from the Internet zone. Therefore, files may be blocked when you click Open in the File Download dialog box. Additionally, after you install 896358 or Windows Server 2003 SP1, Attachment Manager may treat a downloaded .chm file as an untrusted file. Therefore, you may not be able to open the file. These effects are expected and intended effects of installing the security update and of installing Windows Server 2003 SP1.


Warning If you are prompted to open or to save a .chm file from a Web site, you should do so only if you need the file and if you trust the Web site that is providing the file.
In the File Download dialog box, click Save, and then choose where you want to save the .chm file. Then, use one of the following methods:

Method 1

  1. Double-click the .chm file.
  2. In the Open File-Security Warning dialog box, click to clear the Always ask before opening this file check box.
  3. Click Open.

Method 2

  1. Right-click the CHM file, and then click Properties.
  2. Click Unblock.
  3. Double-click the .chm file to open the file.

*Note: This problem (and resolution) is also covered in Chris Crowe’s Blog.

Comments (24)

  1. Madalin says:

    thank's a lot, it really helped

  2. Sloba says:

    Always look that your .chm file is not  in some folder thats named or beggining with   "  #  "  (without quotes)

  3. Alamgir says:

    Thnaks a lot it really helped me. Very simple yet effective solution 🙂

  4. sgislain says:

    Thanks a lot for this, searched for this in swedish but didn't find a solution, method 2 worked for me 🙂

  5. Anup says:

    Thanks alot..:)

  6. anon says:

    jesus christ.

    I literally scoured the entire internet to convert this chm file I chanced upon in an attempt to convert it to a pdf file I could actually open. method 2 worked for me!

  7. M says:

    Awesome.. thanks man.. helped me at the right time..

  8. T says:

    Thank you.. Well-written and complete article.

    Method 2 solved the problem.


  9. o says:

    This is simple and very effective. Thanks a lot. Spectacular job done well  🙂

  10. johnson says:

    Hi i am using vista basic. i dont have the option "unblock" button, suggest me a way to open it

  11. jay says:

    Thanks. Worked. Windows XP. Method 2

  12. tony says:

    Thank you very much. Keep go. All the best.

  13. Byron says:

    Microsoft not much help; if their 'unblock' does not work or is missing- try the following: This worked for me in XP (not sure about Windows 7) Go to Google, search for UniExtract otherwise known as Universal Extractor —it was free last time i looked, download, install, set to include context menus. Then right click a .chm file and the context menu choices should appear if installation was successful —left click on extract to subdirectory, this means that the file will be extracted to a new folder same name as the .chm file. Open folder and your goodie file should be there as an htm, select the initial TOC, table of contents, left click it and it should open in your default browser, use "next" key buttons to scroll thru to your next page, so on and on.

  14. kamil says:

    thanks a lot. simple and informative 🙂

  15. Kibkab says:

    i try the method 2 but another problem happened.What is that haven't Unlock  check box .

  16. Michelle says:

    @Sloba – I can’t thank you enough. I’m on Windows XP SP3. I’m taking a C# programming course, so my folder has C# in its name. Once I moved the file to another folder, I could open it. That’s all I had to do! Thanks a lot!!!

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