Adding a UserControl to a webpart

[joer.banno]

I'm trying to add an existing UserControl to a webpartzone.
I found the usercontrol on:
http://www.codeproject.com/KB/user-controls/rssaggregator.aspx
I'm using the dll, adding it to the bin directory adding a reference
to it and registering it in web.config like this:
<pages>
<controls>
<add tagPrefix="asp" namespace="System.Web.UI"
assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35"/>
<add namespace="AjaxControlToolkit" assembly="AjaxControlToolkit"
tagPrefix="ajaxToolkit"/>
<add namespace="RSSAggregator" assembly="RSSAggregator"
tagPrefix="RssAggregator"/>
</controls>
</pages>

No I can declare the usercontrol within a webpartzone:
<ZoneTemplate>
<RssAggregator:RssAggregator ID="Rss1" runat="server" />
</ZoneTemplate>

But when I run the website, I get this error:
Server Error:
Additional information: The "path" argument cannot be empty if the
"type" argument is UserControl.

So what am I missing?