The message "grants" could not be moved to the mailbox"......".
The message "Grants" could not be moved to the mailbox "..........".
Mail was unable to open the mailbox on the server">>>>>".
iMac 27″, macOS 10.15
Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?
Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.