Description:
Invalid [image_position] : '...'
This means you've entered an invalid entry for image_position.
Solution:
image_position must be:
A positive number
Between 1 and 10
If you use repeat positions for variants of the same listing, the bottom one will take the position. The other pictures will be given the first open position in the order they are listed in the template.
For more information on how images are uploaded visit the How to Upload Images? article.