Photoshop7 not saving/opening PNG files!

This has been a lingering problem. When I try to open a PNG file, I get this error message:

< http://i69.photobucket.com/albums/i50/OperaticXingenue/error message.jpg>

Can anyone help?

Are you sure it it is a .png file and not just a .png extension?

I'm not sure. How would I check?

File > Open As, highlight the file name, and set the file type to JPEG. If it is a JPEG that was simply renamed as a .png this will open it. If that doesn't work try opening it as a TIFF, a PSD, or a GIF. When you find out what kind of file it actually is, fix its extension.