Your image file is damaged. Open it in another program and save it again or convert it to another image format.
I´ve found the solution on another forum: CreativeCOW
I´ll paste here:
Re: PNGIO library error--render failure
by Carl Fontaine on Aug 22, 2012 at 2:10:11 pm
We had the same problem on a project and we finaly found the solution. I'm posting this today because I was searching myself the solution and didn't found nothing on the web.
The problem is: we had a pre-rendered PNG sequence in our AE project, with some broken file (NOT MISSING). It's a 2000 frames background playing in loop. We found that some image was rendered (for unknow reason) like this...
You can see the strange lines at the bottom. It's very hard to see when you're looking at a big sequence in windows and no image is missing. The PNGIO error come up in AE only when you are on that image, in the project. That's how we found which exact frame was broken.
Also, we are rendering on a renderfarm. Maybe the PNG sequence had error because of this...
We re-rendered the broken PNG, restarted the render, and now it's fine!
I hope that help!
I´m experiencing the exact same problem and I just found out that my png sequence is broken too.