I just did a fresh install of Register Plus and found the same issue w/ the Javascript error.
The problem is that if you don’t select the box for “Allow New Registrations to set their own Password”, it won’t output the correct jQuery include. You can fix this by moving line 1317 to line 1379:
<script type=’text/javascript’ src='<?php trailingslashit(get_option(‘siteurl’));?>wp-includes/js/jquery/jquery.js?ver=1.2.3′></script>
Secondarily, I noticed that the custom Registration CSS wasn’t showing up on the page. Turns out this is because this code will only show if you have chosen a custom logo. It can be fixed by moving lines 1550 and 1551 to line 1508 and 1509 right before the end < /style > tag.
<?php if( $regplus[‘register_css’] && $_GET[‘action’] == ‘register’) echo $regplus[‘register_css’];
else if( $regplus[‘login_css’] ) echo $regplus[‘login_css’]; ?></style>
