It's a Samsung Galaxy Tab A. The Google account is the same one that I used to set up the device from new originally - the password has been changed since, but it is not accepting it. The device was bought brand new from O2.
Because the password had been reset, I was told that I had to have a verification code sent to my phone, which was accepted fine by the device. However, when I tried to log on with the new password, I still get the "unable to sign in" message.
The tablet was brand new when it was purchased. I have changed my password, and also received an authentication code from Google, but whenever I try to log on to the device, I get the "unable to sign in" message