Vista - Vista search - preview pane problem

The preview pane in Vista search seems to work intermittently. Many times
it simply won't give any preview at all, even though it may have previewed
that very file just seconds before. This is more likely to happen with pdf
files (I have Acrobat Reader 9 installed) than Office docs, but it happens
with those too. This problem pretty much makes the preview pane unworkable.
Any ideas what may be wrong, or is this a Vista bug?

I have a recent problem with the preview pane too but regarding pictures
It seems to work fine on my side with pdf and word docs and I have acrobat 9
But for my pictures, I use irfanview 4.20
This has been going on for a few weeks now and it's getting bothersome because when I go to personalize my desktop background, it just shows the irfanview logo instead of a preview
I guess I could stop using preview pane and switch my viewing to thumbnails but I don't like that type of view
I always to view them by list and have the preview pane on the side
Usually if I can't see anything in the preview pane, the file is corrupted and wont open, but I've been able to open my files fine so I don't know what's going on either
I tried uninstalling irfanview and reinstalling but I still get the same results