The first things to check are -:
- The guestlist file needs to be saved in csv format, it won't accept any other format
- Have you included email addresses and names? These are mandatory
- Are there any special characters such as accents over letters? These can cause errors
- If you are uploading anything date related - it must be formatted YYYY/MM/DD
- If you have checked all of these and are still encountering errors, it's worth getting in touch with the Support team at help@rmp-connect.com