Its not working because your using the GL/Cashbooks layout. You need to use the Customer Documents Layout.
On the menus click Help...Pastel Help
Click on the search tab and search for this: Import/Export File Layouts - Customer / Supplier Documents
Select the last search result.
This is the correct layout.
You are also not importing from the correct place...
Open Process Customer documents and select credit notes...
At the bottom of the screen click the batches button...this will allow you to select the import file.