Is it a blank area that is still clickable--meaning, is it just the picture that is missing? What is the alt-text when you mouse over where the picture should be (is it "Run this task" or "placeholder.png)? Can you see the task on the Status tab?
Check C:\Program Files\QlikView\Management Service\QEMC\SourceDocuments.htm at Line 175. The line should read:
Actually, start.png should exist in this folder: C:\Program Files\QlikView\Management Service\QMCCommon\Images. Is it possible that the NTFS permissions changed accidentally on some QlikView program files so that the Publisher account no longer has read access on pngs or htms? The account is a local admin, right?
My Status task list also appears and disappears mysteriously. One minute it's there, showing a list of scheduled tasks. The next minute it's completely blank. Seems to disappear/reappear when I adjust document reload schedules. But this is pretty annoying...