iam running a mesh with 3 R510 AP with Unleashed Firmware 18.104.22.168.195.
There should be an AP-Group Option for configuring 11n only Mode.
But there is no such Option. This one is missing.
It's enabled alright... Is this client 11b only? Are you sure it's not connecting with 11g? I'm not an Unleashed user so we might need some help from one of the Ruckus guys. They're pretty good about chiming in.