I notice that your image is not technically defined with a resolution of 72 dpi, but at 300 dpi:

I can’t say definitively that this will cause your problem. Browsers are typically smart enough to display an image with a resolution of 72 dpi (using pixel sizes), regardless of the "Resolution" that is defined in the image. However, it may be worthwhile to re-save the image with the resolution correctly configured for the Internet at 72dpi. Facebook may be confused by the size of the image due to the resolution setting.
In addition, to eliminate potential image problems, if you have Photoshop, use the "Save for Web" command to re-save the image, which will automatically detect the re-saved image with a resolution of 72dpi and save it without a built-in image in the preview you should always do for the Internet anyway to reduce file size. Then try again. Again, I'm not sure if these suggestions will work, but it seems like a good idea to fix the resolution, inline preview, and potential problems with the original file by re-saving.
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