network manager caot deal with manual chael selection on router

I have encountered a weird problem when trying to improve wireless reception in my house.

On my TalkTalk super router (Huawei HG635) I changed the 2.4GHz chael from Auto(9) to 6. Then the WLAN is no longer visible in the network manager. I use kubuntu 14.04 LTS. I also used the LinSSID tool, where the network also no longer appears.

If I manually set the chael to 9, the network is visible, but I caot coect to it. Upon entering the password I get the notification that the network was discoected. Setting the chael to 7 produces the same result as setting it to 9. I have tried rebooting both router and laptop in between changes, to no avail. Meanwhile my Android phone has no issue coecting to the WLAN in any of these circumstances. Only when I set the chael selection back to Auto, the router chooses chael 9 and the laptop happily coects to it.

Any help would be appreciated.