Can't access Google Calendar

I have been using EM client for a while but continue to have trouble linking my Google Calendar. Every morning I start EM client I get an error message asking for my Google Calendar password. When I enter it, it doesn’t accept it though and I have no choice but ‘cancel’.

The whole text of the message is:
Server says "Google.Apis.Requests.RequestError Invalid Credentials [401] Errors [Message [Invalid Credentials] Location [Authorization - header] Reason [authError] Domain [global]]