Questions 'Subject' Cannot be Empty on Business Event/Import Scenario

Incoming emails create Cases. A Business Event monitors Case creation and, when the creating email's subject begins with "New Service Request |", the Business Event launches an Import Scenario to insert additional data (parsed from the email's subject text) back into the Case. Except it doesn't work, and the Business Event History gives "Error: 'Subject' cannot be empty." But if Subject was empty, the whole process wouldn't have launched in the first place because it requires Subject to begin with "New Service Request...." Screenshot of the Import Scenario is attached. Any ideas?

Thanks.