1001 error: customer already exists

1001 error: customer already exists

Hi, I would like to get the XML response after creating a customer with the API, but I keep getting a 1001 response stating that the customer I am trying to add already exists, even though I have tried changing every single information concering the customer I am trying to add and even deleting every customers in the account, making sure there wasn't already an existing customer with the sameinformation.

Why is the API telling me that the customer already exists ? This error prevents me from getting the XML response, which I would like to have !

Thank you,
Francis