cent OS connect using SSH (putty) , login as root
rename maildirsize file and go to cPanel
Now Quota can be easily changed
in other OSs
Login to your server via FTP
Navigate to the path /mail/your-domain.com/mail-username (change your-domain.com to your domain, and mail-username to user that had error)
Find file name maildirsize, the delete it.
CPanel will automatically recreate maildirsize file after deleted.
Update your mail quota using CPanel and error should be gone.