Try this to convert the quotes correctly:
Open bbimport_invib.php and change in line 47
PHP Code:
$post = preg_replace('#<!--QuoteBegin--([^"]*)\+([^"]*)-->([^"]*)<!--QuoteEBegin-->#siU'
to
PHP Code:
$post = preg_replace('#<!--QuoteBegin-{1,2}([^"]*)\+([^"]*)-->([^"]*)<!--QuoteEBegin-->#si'
Are specific html tags not converted in the signatures or are all tags affected?