Help with Thumbs

I have a major problem. I have modified a theme to my liking (cant remember wich one it was).

I have problems with the thumbs. It works great on the site, but when I use wptouch iphone and change the size of the Thumbs in the css file some of my thumbs links to the wrong size. All my images are 600×250 i set 276×115 and most of my thumbs show up just right, but some of them are streched and pixeld. When i check these images they use the autogenerated 150×150 (or smaller) image and that messes things up.

The same happened when I used the popular posts widget.

I dont know any other way to explain this I hope you understand. If you dont please ask me and I´ll try to explain what i mean.

The site is: http://onyanserat.se/

Do you need some more info?

Please help me this is driving me insane.

Thanx

lillprinsen