It should not say that at all, A directory is different from another directory as well as its contents. What is the file name? Do you have a link to the site so that i can view the error.
Maybe a couple of links to different pages.
What operating system is your server? (Windows, Linux)
What server tech are you using? (PHP, ASP, JSP, etc)
This is the very first time i have ever heard of this problem and i have been developing for years. So please any other information would be helpful.
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http://www.htmlhelpcentral.com I am also over then long with many other very skilled web developers.