Some users have both Windows and Linux machines on their LAN, and after deploying Samba sharing on Linux, they find that CHM files on Samba shares cannot be opened from Windows machines. This is actually not a Samba sharing issue, but a security restriction of Windows itself. If the problematic Windows machine cannot open CHM files shared on other Windows machines either, this situation is confirmed.
Microsoft has published a specific and detailed explanation:
http://support.microsoft.com/?kbid=896054
Here I'll document my actual experience in solving this issue. I was using Windows 2003 Server, and this time I installed a version that integrated updates, so the problem of not being able to open CHM files on shares occurred. According to Microsoft's explanation, I first added the MaxAllowedZone setting in the registry but it still didn't work. Later I added UrlAllowList and it worked. Note that LAN shares need to be written in two formats, such as:
"UrlAllowList"="//productmanuals/helpfiles;file:////productmanuals/helpfile"