I spent some time going through the plugin code. Not sure if this is the only thing that fixed it (since I tried some other conversion plugins in the meantime), but the contructor in PhpbbToBbpress.php didn’t have an option for the current version of the bbpress plugin which is now at 2.0.2. I added ‘202’ into the array it does the version check against and the conversion is now running (is currently mering users). Fingers crossed the rest of the conversion goes well.
