If you want to experiment between WPA/WPA2 (or WEP or None), after making that change on your DIR-655 (or any AP), then go to your wireless devices, wipe out their saved settings for your access point, reboot the wireless device, and then associate like you would with a brand-new access point.
This advice cannot hurt, since it doesn't do anything but match the current settings at worst. However, it won't help you connect a WPA-only or a TKIP-only network device to a WPA2-only network.
If this helps, it's because after you changed the DIR-655, the wireless device remembered the previous connection and security parameters which were no longer valid. Following that process creates and saves a new, clean, correct set of parameters reflecting the recent change you made to your wireless network.
Note: If you do have trouble connecting up to a WPA and/or WPA2 network with these steps, its possibly because the AP has the wireless device in an 802.1X lockout or blacklist, earned by too many prior authentication failures. To clear the lockout, repeat the above steps and remove power/restore power to the Access Point right after you reboot the wireless device. If you don't have access to the AP's power, then leaving the affected device offline for a little over an hour or two should also expire the lockout (that's a guess, I don't know where D-Link's thresholds are set).