I have win 10, both pro version and single language version. I checked the firewall and it is still ON but I can not install font. The font I am trying to install is siddam font (http://www.cbeta.org/download/cbreader/siddam.zip).

this solutin worked for me , u can try it guys! https://www.youtube.com/watch?v=GXLFmD6sEwA

What's append exactly ?
Have you read the FAQ ? http://www.dafont.com/faq.php#win

Menhir, his post is 5 months old.

Hi daaams - more like 5 years old... lol

yeah i know, but i was talking about the post Menhir quoted

I'm going crazy! this is exactly the problem I am having. I have tried all of the above solutions but cannot install fonts anymore. My system updated like a week ago and now all of a sudden I have that error message come up on ANY font that I try to look at (even ones on my system that I already have installed). Anyone have any idea ?
the only thing I can think of is restoring my computer back to a week ago.

I am also having the same exact issue.... I tried to go into services and into the firewall but it made no difference. Cannot install any font.
Did you come up with a solution? I don't think my computer updated yet, but I could be wrong