You may have been trying to action an import of contacts with more than 500 contacts in your datafile, but getting the message that your file has too many contacts and you're wondering why you can't action that dataload?
1. You are probably on either the Free or Sales package. The Free package limits you to 250 contacts per dataload and the Sales package limits you to 500 contacts per dataload.
2. You can easily upgrade your account to either the Marketing package (20,000 contacts per dataload) or the Complete package (60,000 contacts per dataload) to make your life a lot easier for your imports of contacts.
If you have further questions about this please raise a Support ticket to us.