Error with "su"

I downloaded the KDE4 Live CD (v. 11.1), and all seems to be fine, except the “su” account. When I try to run yast or any other app that need to use the root account, appears a message saying:

“Su returned with an error”

Then, I go to Konsole and type “su” and it doesn’t let me enter the password, It just show me “su: incorrect password”. And, that’s all. Someone could help me?.

Sorry for my poor english, but I speak spanish.

Tnx all!