This can be caused by having spurious information that is passed over to Accounts Client and Matter Description details.
In Case Enquiry check the name and address details for any special characters such a pipe symbol |, @ symbol etc.
Amend these details to remove them.
If you close the Client/Case down a warning will come up and point you to the number/name of the field that has the issue.
The error will disappear once this is correctly removed.
You will then need to close the case and re-open for all the linked actions to run.
You can then go into the Client Matter Enquiry/General Postings and check if this matter is available to view.
If this does not solve the issue, please raise a new case online and reference the title of this article.