This problem I have is a real PITA and I'm not sure it's me or MCX9.  When creating a net surface with different or any type of entities for each 'along' or 'across' grid members it takes me way to long to create the surface.  On a given 'along' member I will get "Partial chain: Path between first and last entities not found".  I check the chain with "Analyze/chain" and it says the chain is fine, no overlaps, etc. but when I try to create an 'along' member in "Net surface" is gives the error!  I