I was a little quick in answering a quez about Autoyast problem in the software section, but then I saw it was not the same problem.. Me and some customers/ friends had this problem after updating from Yast friday afternoon. After update we recived this error "Su returned a error" trying to install new updates, or start Yast. The solution is here.
http://www.jentin.com/sudoersfix.txt. Yast removed some lines in /etc/sudoers file after the update. Hope this fix will help others with the same problem.