Error message when uploading an attachment within a workflow step

Symptoms
When trying to upload an attachment in a workflow step, an error message occurs.

Error
Server errror in '/' application
Object reference not set to an instance of an object.

Changepoint.Enterprise.KnowledgeManagement.dcKMSubmit.GetCategory() +192

Reason
Changepoint is looking for the knowledge category named 'Attachment' but cannot find it, because it has been deleted or renamed.
 

Resolution
In System Manager, create a knowledge category with the name 'Attachment'. Use this exact name even if your Changepoint typically runs in a different language.