Automatic followup email plugin not finding the siteurl


I've just installed the automessage plugin for scheduled emails. The emails are going out but the unsubscribe footer text shows the follow:

To stop receiving messages from xxxxx Blogs click on the following link: http://unsubscribe/de2cb86129e7d2eee6247ca989a7bdff

It's not figuring out %siteurl% which appears to be set by this line:

$replacements['/%siteurl%/'] = 'http://' . $site->domain . $site->path;

This is on a sub-domain install.

Thanks for your help