ffwebdesigner on "the_content remains empty on category pages"

I've never experienced that problem before.
Setup: custom theme, based on 2011 1.4.

excerpt from the content.php:

<div class="entry-content">
			<?php the_content( __( 'Continue reading <span class="meta-nav">&rarr;</span>', 'twentyeleven' ) ); ?>
			<?php wp_link_pages( array( 'before' => '<div class="page-link"><span>' . __( 'Pages:', 'twentyeleven' ) . '</span>', 'after' => '</div>' ) ); ?>
		</div><!-- .entry-content -->

this part is supposed to output the content on category and single post pages. It does so on single post pages, but on category pages, nothing. Checked the code several times. Same Problem in theme 2011.

You can see the issue here:
http://www.cad-helpdesk.de/sst/solid-edge - no content
http://www.cad-helpdesk.de/sst/was-tun-bei-einem-netzwerkfehler.html - content displayed properly, by the same code