Anyone know where:

$define_checkout_success

is defined?

It's from tpl_checkout_success_default.php, line 74:
<td class="plainBox"><?php require($define_checkout_success); ?></td>

And it's giving me a fatal error:
Fatal error: main(): Failed opening required '' (include_path='.:/usr/local/lib/php') in....

I've upgraded from ZC1.2 and must be missing a file or something.