Can you give us more information about your setup?
I assume that the computer with ARM is still connected to the Dlink switch and the hub is also connected to the same switch via the uplink port.

i.e. [Rio]--->[Hub]--->[Dlink]<---[ARM computer]
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[3 rebadged Dell DARs, 1 Rio Receiver] [JReceiver 0.2.5 and tRio 0.1.6 on SuSE 9.3 Pro]