Do PNG files come in 64-bit format ??

Many years ago I built a program which needs to load PNG files (it was a 
32-bit build using MSVC in case that's relevant and it uses a popular 
library called gdk-pixbuf...)

I've been converting the program to 64-bit - but strangely, I'm finding 
it won't load PNG files any more. Whenever I try to load any of my PNG 
samples, the function 'gdk_pixbuf_get_module()' returns this error:- 
"Couldn't recognize the image file format for file"

I should probably ask this question in the gdk-pixbuf mailing list - but 
before doing that I'd just like to check if there are different 
'versions' of PNG files (i.e. 32-bit versions and 64-bit versions). 
Other formats are loading okay (JPEG / TIFF etc) so I just wanted to 
check. Thanks,

John