^
I don't have a WDTV so I can be sure.
Try googling (or posting here) the exact error message, including any error codes it might list.
Other than that, check your network settings (Encryption type and Authentication) and try entering them manually. To find out your settings either log in to your router (probably 192.168.0.1 in your browser) and look for wireless security settings. if you can't find them then maybe install the firmware to use widgets -
http://www.dlink.com/widgets which will give you the information.