Admin Password Entry box blank

This has been happening to me for a while. When trying to install something the administrator password entry box pop ups, but its blank. There's nothing on it, just the two blanks where you enter you user and password and two blank buttons (should be the cancel and ok buttons).

I attached a picture.

Did you find a fix for this? I'm experiencing the exact same problem.

I'm having the same problem. I even tried reinstalling Snow Leopard disk, hit utilities, but still no luck.

Help!!