[ubuntu] Repeated WiFi Password Requests - Ubuntu 16.04 LTS

Hi All. I've recently upgraded to 16.04 and have since been having the above problem. Although, I had similar, intermittent problems with the older version of Ubuntu (14.x). When coecting to my WiFi network, I enter a correct password, the system tries to coect and then asks me for the password again. Obviously, each time I am inputting the correct password. No problem coecting to the router with other devices such as Android phones. I am unable to access the config of the router - locked down by the service provider, so I am unable to change any of the encryption settings that some previous threads have suggested. Network Manager shows that the coection uses WPA & WPA2 Personal security settings. My laptop can see the default gateway - coects fine via Ethernet.

I am an unexperienced Ubuntu user, so please, if possible, try to use layman terms. My knowledge of Ubuntu terminal commands is poor to say the least. I've looked through toes of threads on this but can't find anything that helps.

Any suggestions, anyone, please?