I have the same issue with SHAREPORT UTILITY installed on PC, and i could see the ext HD ( has its own power supply, not through USB) behind the router (saying available) but when i click on 'connect", it thinks for a while and go back to available.
Router: DIR655
FIRMWARE: A3 , 1.35NA
SHAREPORT Uility: 3.0
under setup tab> USB settings>my USb type is: SHAREPORT (not WCN config..).
then rebooted the router, still its not connecting...
im the ADMIN on the router,