@Virgo 

Thank you for responding, it is much appreciated.

I did not 'set' the channels or width on either of the devices, they were left on 'Auto' for those options. The CPE510 are set up as 'Access Point (AP)' and 'Client'.

There were only 4 options for levels of security;

1) None

2) WPA-PSK

3) WPA

4) WEP

The default when 'out of the box' is None. In this mode the devices communicate ok. When I select option 2) WPA-PSK and create a password (for both devices) they stop communicating.