Your message means that your photo has exceeded the total number of pixels (16777216) supported by Premiere Elements 9 for the still image.
I have gone into full detail on the issue and what needs to be done in post 6 of this older Adobe Premiere Elements Forum thread.
What are the pixel dimensions of the photos that are triggering this message in Premiere Elements 9.0/9.0.1? Also what is the frame aspect ratio, 4:3 or 16:9? What is you destination...DVD-VIDEO standard on DVD disc or DVD-VIDEO widescreen on DVD disc?
This type of message is not present in later versions of Premiere Elements. But, even though the message in those later versions does not prohibit you from continuing as in version 9.0/9.0.1, that does not necessary mean that because you can you should.
We can discuss this further.
I realize now that some of the pictures that I'm trying to get on my movie/slideshow I'm creating are too big.
I reduced the size using Photoshop and it works!
Thanks for the help!