I'm getting "question marks" on some of my dock icons when I try to launch the associated program; one is 3rd party, the other two are Apple (iMovie HD 6 and Disk Utility). Apparently, the aliases aren't connected to the programs they represent. When I throw out ("Poof!") the old alias and put in a new one, the same thing happens: question mark and no launch. What is happening here and how can I rectify it? (I'm running Leopard after having done an Archive and Install).