nik.p

same problem
to fix it change
\wp-content\plugins\wp-ultimate-csv-importer\includes\WPImporter_includes_helper.php line 514
$fimg_name = wp_unique_filename($fimg_path, $fimg_name, $path_parts['extension']);
to
$fimg_name = wp_unique_filename($fimg_path, $fimg_name . '.' . $path_parts['extension']);