If you opened your geocoded spreadsheet and Excel gave you an SYLK error, here's what happened:
It's an Excel bug caused by the first cell being named "ID." You should still be able to open the file and then can re-name the cell to something else, like "id" or "Id."
This is a rare error. You might encounter it if, for example, you downloaded a CSV from a database, directly uploaded it to Geocodio, then tried to open it in Excel.