been trying to do the import data module and its going grand except when i go on to the Data Import: Clean Up Your Import Filesection on it ive clicked the salesforse option in the choises in the box but ive ben asked to give name and email and wont work

ive been trying to wrap my head around this, putting in my work email just keeps saying this ''Error: Invalid Data.

Review all error messages below to correct your data.'' and underneath that under the email section is

Error: Duplicate Username 

wondering if anyone can help?