I have a phpbb3 board and am trying to import to vBulletin 4.
I have tried these methods (between each method I've cleaned up anything done before for a fresh retry):
Create new database, install vBulletin on new database, install Impex, import from phpbb3 database using phpbb_ prefix.
Install vBulletin on same database as phpbb3 board using vb_ prefix, install Impex, import from same database using phpbb_ prefix.
Export phpbb3 database to sql file, restore sql file using mysqldumper (file was 89MB) to localhost database, install vBulletin on localhost using vb_ prefix, install Impex, import from database using phpbb_ prefix.
Export phpbb3 database to sql file, create new target database on localhost and install vBulletin there, create another new source database on localhost and restore sql file using mysqldumper (file was 89MB) there, import source database to target database using phpbb_ prefix.
Each time, I get 3 failed threads and 544 failed posts. Screen from ACP Import page post import: