Login with VB password to drupal not working for new users.

I have been using drupalvb successfully on a drupal 5 site as follows. Registration is handled by VB, all drupal register links removed / redirected to VB - forum users who don't have a drupal account get one created for them the first time they login. This all works fine and is exactly as required.

I'm trying to upgrade the site to drupal6 - i've done the upgrade and all went really surprisingly well. Apart from drupalvb! the recent forum posts and stuff all work fine so i know it can see the VB database ok, but login for VB users without an existing drupal account isn't working. Reading the manual the only thing that stands out is the bit about UTF-8, My forum database is latin1swedish as was the default back in the day when we installed the forum. I'm guessing there is some kind of encoding problem preventing the username or password being read properly from VB?

Do i need to convert my VB to UTF-8?