An issue occurs in a workflow for which an email is sent containing the following message,
"The given system user credentials for workflow [Workflow Name] are invalid. Please update the system user credentials in the Workflow Designer so that the workflow can continue."

To address this, you'll need to access the Workflow in question from the Workflow Designer tool, then enter the credentials for the DocuWare account being used.

Press okay, then the credentials will have been updated.