See also :
Unable to send participants.
Check that the information of the participants is correct. In particular, check that the date of birth and postcode field (for events where cards are mailed to the participant's home) are in the correct format. A common mistake is to import an excel / csv file where excel has changed e.g. the postcode "00580" to "580" or the date of birth "01011985" to "1011985", i.e. removed the leading zero. Save the fields in Excel in "text" format, so excel does not remove leading zeros. We recommend using the excel format instead of the csv format.