A message fails to display properly, or at all.
This is possibly a malformed message.
Try selecting Properties from the Message menu, then Message Source - this will enable you to see exactly what is in the message. You may be able to see some text, or it may prove to be an empty message.
If you wish the MailCOPA email client support team to look at the message in order to decide whether a fix can be applied to a later version, select Forward as attachment from the Message menu, and send it to MailCOPA Support