thumnbnailhandler don't work on all icons

I just had a reinstallation of my system (windows 7 ultimate) and I reinstallend the thumb nail handler to be able to see the image on my psp files.
(I use paint shop XII)

It does work on some icons, but not on all.

I also made sure the first item “always show icons, never show thumbnails” does NOT have a check in the file and search settings.
Strange also is that sometimes an icon does show the imgae and when I get back to that file later is doesn’t show it anymore and I just see the icon.
Also when I click on save and the window opens I can see all the images with a psp extension, so there it does work.

I had windows 7 home (x64) before reinstalling and the thumbnail handler worked great for me with that.
I did restart the computer. I did try to deinstal en reinstall too. That doesn’t change it.

I did look up Cassels psp tip on this one, but it is not talking about some thumbnails not showing up and others that will. I did some research on the internet but didn’t find much about it.

Can anyone help me out here.

thank you