If a change causes problems, you should undo the change.
In this case, others have also reported Snow Leopard issues as well.
Try granting yourself read&write privileges to the Premiere Pro CS4 folder inside Applications.
To do this, right click on the Premiere Pro CS4 folder, then select "get info", click on the padlock on the bottom right and enter admin username and password, then click on + on the bottom left, select your user name from the list and click Select. Then click on Privilege from the list and assign "Read & Write". Also choose "Apply to enclosed items..." from the dropdown list on the bottom (click on the little gear to open it).
Welcome to the forum.
I hope that the info is helpful to the OP. Unfortunately, Snow Leopard seems to not play well with much that is Adobe. Many fora are filled with issues and problems with it. Supposedly, Apple is aware of these and is working on an update to address the issues.
Good luck to the OP, and please report success,
Well I solved it by reinstalling. First I tried reinstalling everything as a normal administrator, but that didn't quite work for unknown reasons.
So I re-reinstalled the entire Master Collection while logged in as Root, which worked and has corrected the original issue.
Great news and thanks for reporting. Glad that it was not Snow Leopard and that you're editing.