The customer downloads the file, opens the zip file and copies the help file contained in the zip file to disk. When he then opens the help file and finds the navigation screen is solid gray result. I read Problems with opening CHM Help files from Network or Internet - Rick Strahl's Web Log. I unblocked a CHM file (fix page 2) of web log. He was still unable to view. Several users are having the same issue. Suggestions?

Windows has pretty much deprecated CHM files and tries heavily to discourage use of them. Anti-Virus tools might actually be blocking them completely if you try to run them directly (as opposed to an installed application loading it for a help viewer).

AFAIK though the Windows Zone Blocking is the only real thing that should be preventing access. Anything beyond that is likely some third party AV or Windows Policy that's interfering.

+++ Rick ---