This is an issue with not having a valid client.
Follow the below steps to attach the correct client:
Select Proclaim Desktop/Main Case Handling.
Go into the Case via the search at the top of the screen.
Look in the screens and see if there is a Client Ref field available in any of them.
Select UPDATE if there is and put the correct client in.
Select SAVE.
If this doesn't stop the message try the below steps:
Open the Client via the search at the top of the screen and select the door to exit.
If an error appears, then the client item attached to that error needs rectifying.
Find the item on a screen.
Select UPDATE.
Amend and click SAVE.
Exit out of the Client and this will update the record.
N.B.
Check Case Type Maintenance and ensure the relevant case type is set to YES in the Update Accounts column.