I was programming and had to peek at some helps when I was stuck in absolutely unexplainable situation. I had these docs in .chm format, so they are actually opening in Internet Explorer, but instead of the text I had to stare at the “Page cannot be displayed” error message. What the hell? My first intents were to blame the security settings in IE (which I do not regularly use and thus have security tied up just in case). So I went and tried all imaginable combinations, relaxing securities to barely protect anything, allowing all possible evils to happen… no luck. Well, there may be some system-wide settings then, so I googled, and googled, and googled… And found absolutely nothing helpful in my case — file was on the local disk, not downloaded from the Internet, permissions were correct — I couldn’t think of anything that should prevent it from opening properly. So I was stuck. Hopelessly I decided to do a very naive thing — to move the file into a different folder — and it worked! Aha, the folder name. There were the C# related docs, so the folder was named C#. I have no idea why but Internet Explorer just hates opening files from folders with # symbol. Ridiculous!