Interpolate curve

I am trying to draw a series of concentric curves which i can then manipulate together (Rhino & GH files attached).  I have 4 orthogonal lines with one central common end point, each divided into 5 segments.  From the Divide function output I have used a List Item to select the second point on each line and fed this into InterpolateCurve (meaning to do the same for each of the five item numbers in the list to create the 5 concentric curves).  But the IntCrv doesn't like it and glowers red at me.  I can't work out why!  Please can someone help me either tell me what is wrong or what I should have done to achieve this? 
BTW Grasshopper has crashed twice on me while doing this, precisely when Rhino does its autosave - is this a bug??
Many thanks, David