My crystal ball suggests that maybe you're using a newer version than the PB? If so then no root is enabled, and you need to do that in NetInfoManager (or better yet, just use the sudo command -- much safer). If not, search these fora and the others for how to get back a lost root password (known problem with PB, there are many posts about how to fix this.)
So reply back with some more details aout your problem (when did it start.. what system, what OS build, etc.) and maybe someone can help.