We integrate with a normal vb3 install. If you have a custom style you would need to define the relative image paths as full url's or modify our header-include autorewrite code to also rewrite your custom image directory. By default we are not going to know where those images are unless you have full urls to them.
Next your login. Classifieds and Forum cookies must be set exact.
cookie path /
cookie prefix bb ( this is usually in the vb
cookie domain .domain.com you want the dot so it works with or without the www so you dont drop login on either product
Next the correct vblicense number must be entered in the config-inc.php file for login to work. This is license number not customer number.
So if you can get your admin page up in classifieds check the cookie settings and make sure they are exact as posted and check the license number in the config. Correct any issues. You can then go to the forum admin and correct any cookie settings.
Clear all cookies and relogin in you should be fine.