iis web.config url rewrite and 2.9 and permalinks

This is a wierd problem not sure if it’s my system or wordpress so i’m just going to ask if anyone has a similar situation.

images are coming back with errors and can’t find if I turn permalinks on.

for example

http://frumph.org/wp-content/uploads/2009/12/chick2-150×150.png

will show just fine, but

http://frumph.org/wp-content/uploads/2009/12/chick2.png

comes back as a 500.50 error, this didn’t happen previously in 2.8 and subsequent svn’ 2.9s when the_post_thumbnail was the_post_image and everything was released.

Has anyone else seen an issue like this?

note: if I turn permalinks off, it works just fine.