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Wierd? Anyway, on Windows 7, I've downloaded a CHM file on the desktop and unblocked it by Property > Unblock.

I moved the CHM file to a folder on the desktop to organize the files, and when I opened the file, the content of the CHM reader couldn't open the pages in the CHM file. I've open the file property, but the unblocked button is gone. Well, I can simply download the file, though I find the problem interesting and I need to know how to troubleshoot it.

So, how can I unblock the said file?

Update Clarified location. I was referring to a folder in the desktop, not in network drive.

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"Then I moved the CHM file to another location and" Is the other location on a network drive or another remote place? – user4711 Jul 19 '12 at 6:19
What is the name of the new folder? Related:… – iglvzx Jul 19 '12 at 6:31
LOL! I've placed my chm file in desktop/MS/C# and it appears that the # sign affected the access of the file. I renamed the folder to CSharp and the issue was resolved. Thanks, @iglvzx – OnesimusUnbound Jul 19 '12 at 7:10
@OnesimusUnbound No problem! As mentioned in my answer, the CHM tool hasn't been updated since 2002, so there are unfixed bugs like this one. :) – iglvzx Jul 19 '12 at 7:38
possible duplicate of Can't read .CHM file in specific folder – Bob Jul 20 '12 at 7:49

Maybe it's not on a local drive? If so, you can allow the viewer to show chm files on a network drive:

  1. Start -> Run -> Regedit
  2. Search key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x
  3. Create subkey ItssRestrictions
  4. Create DWORD MaxAllowedZone with value 2

This should fix it.

You may find this useful:
There is a table which shows the zone levels.

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Worked, but i had already added the drive letter to the intranet zone and lowered the security level. Further i had already run icacls P:\APPS /SetIntegrityLevel (OI)(CI)M Adding same parameters for just the user HKCU fails. – rjt Jun 14 '14 at 1:31

you can do it through powershell

  1. Start a powershell prompt
  2. write "unblock-file ", do not press enter
  3. Drag the file from explorer to the powershell prompt (to get the filename)
  4. Hit enter.

the file should now be unblocked.

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