Box Alignment

Hi,

I'm very new to Kangaroo and have some very small success in getting it to work, however this time the intention for me is pretty complex and I'm unsure about why this script refuses to run.

Basically what I am trying to do (or what I'm working up to) is randomly generating these boxes, then moving them towards each other, basically a packing algorithm. I know the next step will be the make the boxes rigid so they do not intersect but for the moment all i want to do is have them move towards each other. I've tried atm to make the corners of the boxes the attracting elements for now, then use the median points of each as the lines they will follow. I'm getting the following runtime error

1. Solution exception:Index was out of range. Must be non-negative and less than the size of the collection.

Parameter name: index

No idea what that means. Any help would be appreciated and if anyone see anything glaringly wrong with the script asides from what I've mentioned I would appreciate it being pointed out too

Cheers