PowerPoint 2003 - Application Error

After running a custom Windows Update a few days ago, I am now receiving an error message when opening various PowerPoint files: "PowerPoint" was unable to display some of the text, images, or objects on slides in the file, "filename," because they have become corrupted. Affected slides have been replaced by blank slides in the presentation and it is not possible to recover the lost information. To ensure that the file can be opened in previous versions of PowerPoint, use the Save As command and save the file with either the same or a new name." When I click OK, the file opens and it appears that all of the text slides have text boxes with white backgrounds where in the original versions the backgrounds were clear. I am unable to change these and the application stalls when I try to modify. I tried Detect and Repair and this did not solve the problem. I tried opening the files on other computers, and the same error message occurred. I am afraid to open other files that I need to use to create new presentations.

I have Windows XP Pro, and the version of Office /PowerPoint is 2003, SP3