Sudden problem syncing calendar with Thunderbird

About 2 days ago, Thunderbird sync with my icloud calendar has been failing. This is the error message:

A username and password are being requested by https://p05-caldav.icloud.com. The site says: "MMCalDav"

I retype the info (though had previously had password manager remember it), but the same message keeps coming up.

I can access the calendar on my phone, also icloud via a browser.

Any ideas?