That error is a pretty non-descript SKILL error caused by something doing append(someArg t) in SKILL code. Could be anywhere. You could try doing:
and then opening the layout. I'd be pretty surprised if it was anything to do with it being IC615 layout - but maybe you have some customization which is looking for something specific in the layout and not handling things well? It might be Cadence code, but I've not seen this before (with these symptoms, at least).