I recently upgraded to 0.8.6 but it wasn't able to find the recommended version of auth_wpbb.php and common.php in the configuration, so I wasn't able to use the plugin. The same thing happened with 0.8.7 and with one change I was able to fix the problem.
On common-functions.php, I had to replace:
'source' => realpath(__DIR__ . '/files/auth_wpbb.php'),
'source' => realpath(dirname(__FILE__) . '/files/auth_wpbb.php'),
'source' => realpath(__DIR__ . '/files/common.php'),
'source' => realpath(dirname(__FILE__) . '/files/common.php'),
Also, the end ?> was missing on auth_wpbb.php.
I am using Windows 2008 Server with IIS 7.
Thanks a lot for a great plugin!