imageserve.inc producing fatal libpng error

Hello,

I just migrated a site and this notice is displayed with every page load. I understand the method is triggered to place a small transparent png on cached pages to record impressions, what I can't figure out is why I am receiving this error where I had not in the past.

warning: imagepng() [function.imagepng]: gd-png: fatal libpng error: Invalid number of colors in palette in /var/www/html/dev.drupal/sites/all/modules/ad/imageserve.inc on line 57.warning: imagepng() [function.imagepng]: gd-png error: setjmp returns error condition in /var/www/html/dev.drupal/sites/all/modules/ad/imageserve.inc on line 57.

Any thoughts?