Error: Content is not allowed between the opening and closing tags for element

[Allan Ebdrup]

I have a ascx webcontrol that I register with:
%@ Register Src="../Controls/Default/Library/Basket/Basket.ascx"
TagName="Basket"
TagPrefix="uc1" %>

and instantiate on the page with:
<uc1:Basket ID="Basket1" runat="server" />

This works without problems, Now I've added the attribute:
[ParseChildren(ChildrenAsProperties = true)]
to the basket control and added a property called Header of the type
ITemplate.
When I change my basket tag to look like:
<uc1:Basket ID="Basket1" runat="server">
<Header>Myheader</Header>
</uc1:Basket>

I get the following error on the Basket tag:
Error 1 Cannot switch views: Content is not allowed between the opening and
closing tags for element 'Basket'.

And the following error on the Header tag:
Error 2 Validation (XHTML 1.0 Transitional): Element 'header' is not
supported.
When I run the page it works fine.

What am I missing to allow tags inside the Basket controls XML?

Kind Regards,
Allan Ebdrup