Every time I open up eM client, I am prompted for my username and password for the account. Even if I log in correctly, the box continues to pop up every few seconds asking for the password, or with some error. At first I could tolerate it, but now it has become plain annoying.
Majority of similar issues is caused by account misconfiguration so I would start with doublechecking the account settings. You can also try to recreate the account and if it won’t help, send us your CalDAV logs. Thank you.