Wordpress full size image error 500 on IIS 7.5

I'm using wordpress on my Win Server 2008 R2. When I try to view an uploaded image, I get error 500. All the small preview images work.

Working:

/wp-content/uploads/2010/09/image-60x60.jpg
/wp-content/uploads/2010/09/image-100x100.jpg
...

Not working

/wp-content/uploads/2010/09/image.jpg 

I have checked that directory and that file exists. When I open that image with paint and save it without editing, it starts to work and no error 500 anymore.

What could be the problem? Is something breaking the image when uploading?

From serverfault Mika Kolari

• This is probably a permissions problem related to the temp folder where images are uploaded to. Check this blog post which will almost certainly be your same problem:

  http://licensetoolkit.com/blog/errors-with-images-in-wordpress/

  HTH, John

  Mika Kolari : Yes, I had the same problem. My solution was to change the anonymous authentication from 'IUSR' to 'Application Pool Identity' and define a new application pool. Now the files have permissions defined for that application pool. I still wonder why IUSR didn't work, because it did have permissions for that file.
  From John Patterson