Today’s odd problem comes from the Super User forums. User void.pointer reported that they were unable to preview or install fonts on Windows 10 x64 Pro. When you right-click on the font and choose Preview, it gives the error: “The requested file [font path] is not a valid font file.”
Upon trying to install the font, they receive the error message:
“Cannot install [font file name]
The file ‘[font path]’ does not appear to be a valid font.”
The problem was consistent with several otf and ttf fonts, eliminating file corruption. I was not experiencing the issue on my Windows 10 x64 Professional computer but others were and eventually discovered a solution. The original poster and those also experiencing the issue had turned off Windows Firewall. Upon turning the service back on, they were able to install fonts again. To cause the problem, it requires disabling the Windows Firewall service (Changing from automatic) and rebooting. Anything less, still allows fonts to be installed.
I’m not sure why you would turn the Windows Firewall off for longer than just testing but apparently a few people do and disable the whole service, not just turning it off through Control Panel. It was also reported that you are able to disable the Windows Firewall again after installing the fonts and they will remain. It is unknown if a replacement corporate software firewall would interfere but it seems as long as the Windows Firewall service is not disabled at startup, everything should be fine. There is some thought that it might be related to Unblocking the font file (right-click, properties, Unblock) may remove the requirement for the Firewall but this was disproven.
It’s possible that Windows was trying to prevent a security risk of allowing Internet files to be added to the System32 directory directly but why not give a better error message then that indicates, “You must turn on the Windows Firewall in order to install this font.” Another user found a connection in the Event log stating “App Container microsoft.windows.fontdrvhost is unable to register with Firewall.” It would seem Windows App Container service relies on the Firewall to function but a better error message certainly would have helped.
Image credit: void.pointer