I just installed eM Client, I connected my two gmail accounts and I get the error that is displayed in the screenshot attached. 
Did you use the automatic email wizard in EMClient to connect your Gmail accounts or did you add the accounts manually. Also did you get the Gmail (Allow) authentication button at the end to authenticate those gmail accounts.
Yeah I used the automatic wizard, the window opened in chrome and I clicked accept.
Ok. Do you have any optional firewalls / security programs installed ?
Nothing other than what Windows 10 already have. It’s a fresh install.
Check that Imap is enabled in Gmail
Open Gmail via the web browser
Click on the “Cog” icon in the top right corner.
Then click Settings on the menu .
Click the Forwarding and POP/IMAP tab.
In the “IMAP access” section, select Enable IMAP.
Click Save Changes.