I’m having the exact same issue, but instead of importing the vbulletin database directly from vbulletin server, I have exported the vbulletin database as a sql file and imported it over to a new database that I have created on my server where my WordPress and BBPress installation exist. I have entered the following to each of the import fields:
Platform: vBulletin
Database Server IP or hostname: localhost
Database Port Use: 3306
Database Name: [entered correct db name]
Database User: [entered correct db user]
Database Password: [entered correct db password]
Table Prefix: blank
Once I click the start button, it will show “Starting Conversion” but just hangs there, any idea what I’m doing wrong?