Ok, thanks for sharing this info.
I was told that Sony has issue with D-Link routers and this could be what is holding a fix up. The issue is between Sony and D-Link is all I got.
I don't know if or when that will be resolved.
I recommend that you use WPA and TPIK for now. If you need better speeds on 2.4Ghz for other devices, as a suggestion, you could connect up a 2ndary 2.4Ghz AP and use it for all the other devices to connect to it using the N mode configuration with WPA2 settings, or set up the new AP specifically for the Sony device only and change the 5500s radio settings for all other device to use. The SSIDs should be different as well as the channels. This is a work around suggested solution until Sony and D-Link get this fixed.