mmm I suspect that this is a generic catchall that lets you know something is not working. Go to Site Admin > Development > Debugging and turn on Debug Messages: ALL ..... Error Messages. Try the upload again and see what happens. If the error recurs, go to Site Admin > Reports > Logs and select the (Site) option and then select Site Errors and see what the report is telling you. Is there any more information there? If not, then have a look at your PHP error logs, see if that is telling you anything more.
The only other alternative I can think of lies with what you are importing. Where are your sourcing it? Externally or from an older course? Is an import action appropriate for what you are trying to achieve?