Is your phone on 5 GHz actually getting an IP address via the DHCP or not?
If so then are the Gateway and DNS entries correct?
Does it say why it can't connect?

Neil..

Not getting any IP address, just comes up with failed to connect.

I may reset the units to factory and try and connect with standard preset details.

Sounds like your 5 GHz side is not seeing a DHCP server for some reason.

Neil..

Check your firmware version and ensure that it is either 1.1.7.1 or 1.1.8
I have just seen in the release documents that there was a problem with not passing DHCP packets to 5 GHz clients when SSID2 had a VLAN tag specified, it is in the 1.1.7.1 update documents.

Neil..