Hi Charles,
Concerning your question 2: A singular element is one which is locally inside out. Ideally, they should never occur, but they do sometimes in locations where the geometry is particulary poor. If you file a ticket for these models with technical support, then we in development can investigate the details and hopefully modify the meshing algorithms so these problems occur even less frequently.
In general, we have found that it is more challenging to mesh models that are imported into Creo than ones that are created orginially in Creo.
Tad Doxsee
PTC