archives page doesn’t display without putting index.php before it

I used the pages feature to create an archives page, using the archives.php file included in the template folder. I want the url to link to the archives page to be:

http://www.clioweb.org/archives/

But that link will take you to my homepage, whereas this link:

http://www.clioweb.org/index.php/archives/

takes you to the archives page. This is the only page I’ve created in WordPress that does this. All of my other pages work…see for example:

http://www.clioweb.org/links/

I’ve tried redoing my permalink structure, with no luck. Thanks in advance for any help, and let me know if I need to provide more information.