Using this file path worked to list the files but they still are coming in as txt:
/home3/pmi374/public_html/wp-content/sermons
If I just use /public_html/wp-content/sermons I get:
Warning: scandir(public_html/wp-content/sermons) [function.scandir]: failed to open dir: No such file or directory in /home3/pmi374/public_html/wp-content/plugins/download-manager/modules/server-dir-browser.php on line 89