In some cases, the username and password you use for your Google Account is incompatible with ClientLogin and login will fail. e.g. This will happen if you account is using 2-step verification. (ClientLogin is the authorisation mechanism used to log in to your Google account.)
If this is the case, an Application Specific Password can be used.
An Application Specific Password is a password that you can use in place of your normal password to log in to Analytics Pro.
In order to generate an Application Specific Password, see the following guide on the Google Website, which explains the process in detail.
Signing in using application-specific passwords 
The key steps required to start using an application specific password are:
