[TYPO3] Problems with categories in tt_products

[Jeroen Visser]

Dear colleagues,
In tt_products it is possible to generate a list with product categories
and/or a selection of these categories. The page source shows the following
info:

<!-- Plugin inserted: [begin] -->
<div id="tx-ttproducts-pi1-listcat"></div>
<!-- END: tx-ttproducts-pi1-listcat -->

<div id="tx-ttproducts-pi1-selectcat"></div>
<!-- END: tx-ttproducts-pi1-selectcat -->
<!-- Plugin inserted: [end] -->

The problem is that no categories are displayed although they are added in
the back end. The plugin also has the appropriate start point. And I have
copied the template file of tt_products to mu own template folder which I
have described in the constants. Does anyone has a idea of what I am missing
here?

The configuration that I use is TemplaVoila 1.1.0., Typo3 4.0.2. with
tt_products 2.5.2.

Thanks in advance for the reactions.

Kind regards,
Jeroen Visser