Run it in DEBUG mode and scroll through to find the image error. (as well as any others)

This could also be caused by a 'blank' NONE image. It's best to at least have something in the image field - even if it's a 'Image Soon'

Although, you should have an image on each product... Makes it easier to compare products when people are looking.

If you used the easy-populate add-on, do a full export and you can find it that way as well - scanning the 'image' column.

Good luck.