AppleShare IP is not able to use some characters for file names in web server. The server has this restriction for compatibility with other computer operating systems These are protected characters under some OS's and can't be used for file names.
The characters that you can not use for a default file name include: / | \\ ' ] > ; [ < : { } _ = + ! ~ @ # $ % ^ & * ( ) `
You can name a default document using many of these characters in the Finder, but once you try to change the name in AppleShare IP you will not be allowed to do so.
Note: The space can be used in the default document name but it is not recommend.