Please be sure you are using the correct login email and password when you are entering it into Bid Maximizer.
When you apply for a Google API Token, you will open a new API account called "Google My Client Center". You are requested to use a different Email address for your API account(My Client Center) from your normal Adwords account.
With Bid Maximizer 4.0 or later there are two options to log-in to your account.
1-“Using Adwords Login Details”:
If you are an individual user, only managing your own account, then choose this option.
You can enter your AdWords login details into the program and your API Token “a.k.a. developer token” .
2-“Using My Client Center Login Details”
If you are a PPC service provider and managing many accounts under your “My Client Center”, then please choose this option.
Program will ask you the “Account email” associated with the account you want to manage. You can click on “Get Account email” and program would bring all the emails associated with all the accounts under your “My Client Center”.
Click here for the explaination whether you need to use your own Google API Token