First, check that your smartphone or tablet is wirelessly connected to the DIR-505. Sometimes these devices switch wireless networks without notifying the user.
Next, in the SharePort Mobile app, tap on the Gear icon in the top-right corner to access the SharePort Settings.
Ensure the User Name and Password for your DIR-505 is entered correctly (NOTE: This will be the user name and password used to log into the DIR-505 web interface, and not the wireless name and passphrase.)
If you are still unable to view the contents, reboot your device and open the SharePort Mobile app again.