@HGREGG, the upload screen warning you if your photos have different zoom levels or different aspect ratios isn't what Kris is reporting above, but even if it were, the warning wouldn't stop you from uploading the images.
What Kris is experiencing is something like this. (I'm making up numbers for the example.)
1) Add 50 photos to create a walk from.
2) All 50 photos successfully upload.
3) Photosynth examines all 50 photos for image features, tries to match those features, and does some triangulation to try to determine where each point which has been identified in three or more images is in 3D, relative to other observed points.
4) Some of the images can't be matched to the others (perhaps the first 8 images in filename order, four more sprinkled throughout the group of 34 photos which did match, and the last 4 photos alphanumerically).
5) This results in a synth with 34 images, which may confuse the synth author as to where their other photos are.