Hmm. Recommendation for a single prop -- unless it's 'pointing' in a particular direction -- for instance, a spear that you modelled sideways -- use yzx or yxz as your alignment. This way the prop's 'twist' makes it spin like a top which is the most natural way to handle it. I think the message you got is sounds like what happens when you skip a vertex and double another one, like xyx -- which can be done, but I think, if I'm not mistaken, PHI import hates it.