So the software do what it is supposed to do, some instructions are ambigous, so the user produce errors, not the software. But the support is excellent, an very reactiv! Problem solved in 5 minutes!
Note: In the options of the migrationprofile, where you are asked to insert the db prefix, you had to insert the prefix of the wp or drupal tables not the prefix of your joomla tables.
thanks to daniel for his support!