ALGOR didn't have have a problem with it at all. I did the same part in Inventor, and no problem again. I just saved it as a IGS - 144 (Solids as Surfaces) after deriving the midplane surfaces of the part.
Thanks for the help. Shame on the withdrawal based on an irrelevant topic and non-due consideration. I have no idea how a Lord/Peer will help, but thanks for that suggestion which I will follow by contacting Lord Broers (Life Peer) in the the UK House of Lords and mentioning to him that you referred me.