You will only be able to Sign in if you are listed on our website and you have submitted your Google+ user ID to the administrator.
To find out how to find your Google+ ID please see this video here.
The login on Google Chrome works sometimes and other times it doesn't. Windows user try Microsoft Edge browser (I can't believe I'm recommending it).
If it doesn't work then try a different device.
For me on Chrome I tried to log in, it didn't work. So I let it site for about 3 minutes and tried again, then it worked.