Check that all the fields on the excel file you are trying to import are also on the registration form (to do an import you need at least on you file: last name, first name and email address). If not, create them on the registration form and launch again the import.
Download the error report, check what errors are indicated and make the needed changes on your excel file.
Contact Evenium support (+33 1 47 70 90 35 / support@evenium.com)