My products are not showing up with a featured image.

I have been trying to go in and add a featured image to each of my users products. However, I'm getting this error instead of pictures:
Warning: array_combine(): Both parameters should have an equal number of elements in /home/dspinner/public_html/wp-content/plugins/marketpress/includes/common/template-functions.php on line 2840

Could you take a look?