I constantly get an error message that looks like this. It interrupts everything I do. No matter how many times I put in my correct password, it comes right back up. However, EM Client continues to work absolutely fine otherwise. Emails come in and go out with absolutely no problem, yet this insistent box keeps telling me that something is wrong. It is driving me crazy!!! Help!! 
Hi Lora,
This is the most asked question in this forum (strange that a solution didn’t show up when you looked for it).
Anyway, you can suppress this error window as follows:
Tools > Settings > General > General
Uncheck “show window when an error occurs”.
screen shot:
Hi Lora, if you see this pop-up again, try to delete the @yahoo.com part from the “User name” fiedl. Click ok and the account should be working properly then.
Hope this helps, let me know if you have more issues with this,
Paul.
I’m having a similar issue but this isn’t just an annoying error message the out going mail isn’t sent what’s the deal
Hi Mike, what version of eM Client are you currently using? Can you please make a screenshot of the exact error message?
What mail service are you using in eM Client?
Thank you,
Paul.
Hi guys, thanks, this works
Tools > Settings > General > General
Uncheck “show window when an error occurs”.
screen shot:
I tried this and it still pops up… And also pops up when I click on “receive all.” If this has been a problem for years why hasn’t it been fixed? BTW I am new to eM (after years of using Thunderbird, which has finally driven me away), and I would hate to have to try finding yet another client to workk with. Would love some help!