Heh, I have some obscure things that probably won't help, but might anyway!

You could...

Clear your cookies
and/or
Clear your cache (also known as your "files")

Although those probably won't do much. Another thing, are you going file>save as> and then saving it as .png (/.jpg/.gif)? Or do you think you might be attempting to save it as a transparent object?

And you mentioned you are using photoshop, make it 100% sure that it is a flat image. Try going layer>flatten image again just to make sure, and then saving it again.

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