Yes i have been getting this issue as well. it keeps geting the pop up. what is wrong ? I believe my account has the correct passwords and settings. it was working fine for a while and then the server says Authentication failed
Hello Bryan, what mail service are you using with eM Client? Have you changed your password recently? What version of eM Client are you currently using on your computer, can you please check the exact release number in Help > About?
Can you please make a screenshot of the issue and submit the screenshot to us here on the forum?
Thank you,
Hi, i have the same issue with both my calendar and contacts… email works fine… i’m running 6.0.22344.0 and haven’t modifyied anything in the last few months…
Hello Daniele, can you please try to re-setup your account in eM Client and check if the issue persists? We’ve came across this issue quite recently, but it seems this might be related to Google shutting down the support for older authentication methods, eM Client is currently supporting OAuth 2 as the current authentication standard for these services, but for some reason was affected by the change inevitably.
Resetting the account should allow you to use both Mail and Calendar features without any future issues.
Regards,
Hi Paul, solved 
it was an authentication issue
tyvm!
Hello again, glad it works, please make sure to let us know if you come across this or any other issues or questions about the application, we’ll be happy to help.
Regards,