"The page cannot be displayed" error for chm files

I had some chm files that I've always been able to open and read.  However, recently I moved them to other folders when all of a sudden I was not able to view the individual pages in these files.  I got a page cannot be displayed error.  It turns out that the reason is that I placed these chm files in a folder that had a "#".  These were C# books, so I created a folder called "C#"and placed the chm files in this folder.  This is what caused my problem.  Once I renamed the folder to "C Sharp" I was able to open the chm files.