I have never had this problem before with this script and when I came back to Rhino today to have another look, I was getting this error. It seems this is a Rhino error rather than a scripting error? Is this due to an update? I have internalised all curves at the beginning.
Parametric Streets.gh (25.1 KB)
Thanks
I have the same issue 
It was working a couple of months ago but not anymore
Hey James,
After 2 days of non-stop trying I figured it out. somehow clipper library is deleted from your system. I also had another issue with python (I modifed it a bit). So I reverted everyting to default and downloaded “clipper_library.dll” and placed it in DecodingSpaces plugin folder and now it works