Show cart link in popup is empty

[BjornOnPole]

Hello,

URL: http://happy-home.nl/
VirtueMart version: 2.0.18a
Joomla version: 2.5.9

After adding a product to the cart, the popup appears with a button to go directly to the shopping cart.
However, the url in the popup is empty.
When I inspect it with Firebug I see the following:
<a class="showcart floatright" href="">Verder naar afrekenen</a>
*Verder naar afrekenen = Continue shopping

As you can see the href is empty, so that's the reason it won't work.
However, I also have a Shopping Cart Module, that when clicked also show a popup with a button to go directly to the shopping cart.
That one does work!
When I inspect it with Firebug I see the following:
<a class="floatright" href="/winkelwagen.html">Verder naar afrekenen</a>

As you can see the href is pointing to /winkelwagen.html which is the correct page.

How can I fix this problem? I do not know which file to edit to edit the generated url in the popup, please help.

TIA!