Hi,
Yesterday I had the same problem and I solved it.
In my case, I have Prestashop 1.6.1.4 and PHP 7.
You have to change one line in /controllers/admin/AdminImportController.php
Go to line 1006 and add & in variable $user_data
if (!call_user_func_array($funcname, array($row, $k, &$user_data))) {
That's all