DFP Async out of the box?

Hi there, I’ve installed the Ad Code Manager plugin, added an ad onto Google DFP and added the ACM widget into my header. I’ve created a new Tag into Ad Code Manager with my ad tag and my publisher ID and saved it. I load the site and there’s a blank space where the ad should be.

I look at the source of the page and where the ad should be I see this:

<li class="widget widget-header"><div id="acm-ad-tag-%tag_id%" style="width:%width%px; height:%height%px;"><script type="text/javascript">
googletag.cmd.push(function() { googletag.display('acm-ad-tag-%tag_id%'); });

    </script></div></li>

So it seems that the variables in the % signs aren’t being replaced as they should. Do I need to add any additional code into my template in order to get the replacement to work correctly, or am I just doing something monumentally idiotic as usual?

Thanks in advance!

http://wordpress.org/extend/plugins/ad-code-manager/