The second line in the ERC code is for the controlling figure. I am guessing that it has to BE a figure if you cannot get it to work on a prop. Poser 4 will change the figure on file open anyway and I was not able to get at it using a JNT pose - one of the few things that seems to be resistant to pose file adjustments. You need a controlling figure and a controlling group- A prop is a group, so there is a bit of ambiguity - computers tend not to like ambiguity.