Object reference not set to an instance of an object in Pack Objects

I have seen this error message but none of the posts match my specific situation. I am using pack objects to organize my parts for laser cutting so I have a list of objects and a list of planes. When I feed the lists to pack objects I get the error “solution exception: Object reference not set to an instance of an object” from Pack Objects.

After chopping the lists I find that the problem is when index = 14. But then pack objects works fine on both parts of the lists when I split the lists. would like to understand so I don’t have to work around.

using Rhino 6 on a Mac.

Thank you!

Michelle

error obj ref.gh (84.7 KB)