Here are some of the common errors and solutions:
File not uploading at all
Check to see if the file is formatted correctly and is saved in an accepted format (.csv, .xls, .xlsx). Double check that the headers appear on Row 1.
New products are not being created
New products are being created instead of existing products being updated
One or more attributes are not updating
Imported products already exist as Inactive
Spreadsheet contains duplicate Styles
Double check that the combination of Style ID, Option Code, and Size aren't used multiple times within the same document.