Setting up a 2.4 GHz network with Experia Box V10

Hello, apologies for this post in English. I am trying to set up an extra 2.4GHz WiFi network in my home on the Experia V10 Box (Firmware Version:v5.00.61 build511).  I have followed the instructions in the knowledge base. However the box does not save the settings and so the network is not set up. I toggle the switch to select the extra wifi network (see picture),  however when i press save, the switch toggles back to the off position and so i cannot set up a 2.4GHz network? thanks in advance for your help.