Using vB4 Importer 3.6b2, I tried several times to migration a rather large database ( ~200K users +500K posts) from a VB 4.2, However, each time after migrating the users the screen just dies and when I try to resume importing by pressing 'Continue importing' button, I get a 404 error.
As someone has suggested here, I added ini_set('display_errors', true); to /library/config.php. but I don't see any error message. I use nginx+php5-fpm on a 64GB ram server and I set memory_limit to 41280M in php.ini and max_allowed_packet to 40G in my.cnf to make sure that no memory shortage cause this.
I really ran out of idea so that I gave up and now trying to import data using raw sql query. I really appreciate your hints, either to fix the importer problem or to use approprite queries to do the job.