Adobe Reader X changed its DDE server and left the registry dirty behind.
http://www.agmonim.com/2010/12/texniccenter-and-adobe-reader-10-x/ helped to get DocClose working again, I needed to do the registry hack described below the caption "Update!" on that page.
I also made some research on making DDE work. As it is written in the above cited post, changing the server name to "acroviewr10" did the trick for the preview. However, it does not close the document before rebuild. As this computer is a fresh install, no previous version of Adobe reader was ever installed.
It is even more strange for me, that if I change the command to "" for the rebuild, it does not open the document (while executing the same command for the preview does the trick). Therefore I think that the command associated with the rebuild is never executed. Could someone comment on this?