Excel 2007 - PNG images

I am trying to insert a PNG image into Excel via the Insert->Picture button in Excel 2007. When I select a PNG image file nothing happens (IE no image is inserted and no error message is displayed). When I select other image formats, such as BMP images the images are inserted correctly. Inserting PNG images used to work in Excel 2003... Any ideas?

UPDATE:

I downloaded the first PNG I found on the internet and verified that Excel correctly inserted the image via Insert->Image, HOWEVER, the specific image I was initially trying to insert still does not work, and it DID work in Excel 2003... Maybe there's something wrong with the image itself? I'll attach the image here in case someone has an idea...