Have you checked the "plugins" settings in your Admin
App Settings ->Plugins and made sure that the "Categories Skin Tag" is enabled.

Ho John,

yes, it is active by default.

Any other ideas?

Thanks!

The website is http://blog.wifi-wue.de

Ok... check your _main.php for your "custom3" skin against the _main.php for the default "custom" skin... especially the sidebar stuff.
You must have

<?php // -------------------------- CATEGORIES INCLUDED HERE -----------------------------
		// Call the Categories plugin:
		$Plugins->call_by_code( 'evo_Cats', array(	// Add parameters below:
			) );
		// -------------------------------- END OF CATEGORIES ---------------------------------- ?>

Then check your files on your server and make sure you have the current categories.php uploaded under the /skins/ directory

Silencer : You would think that the categories are active by default..
But check it again in the admin panel.

I found a glinch where the plugin came inactive after doing something (not yet found out what you have to do to make the plugin disabled)

@Topanga:
I deativated it and then reactivated it again. No difference, it is still set to active.

@John:
There have only been minor changes to the main.php. The code snippet I posted is identical to yours and from my customized file. The parts before and after look identical to the original main.php

Furthermore, the categories.php is in the skins folder (the most recent one from the download).

Sorry...

I have tried a couple of things, but it even doesn't work with original Designs. Can it be that there has been a problem that results from the upgrade statement?