Arcmap 10.2 "The index passed was not withing the valid range"

I'm testing our product on 10.2. I am running the Polygon to Raster tool and on some shapefiles I get an "The index passed was not withing the valid range" error. This works fine on 10.0 and 10.1. I have run the check geometry tool and there are no problems.

Any ideas, or could someone at least explain what the index is used for?

Thank you.