It would seem that the assembly reference geometry does not work.

I'm simply trying to position a smaller part on the surface of another larger part. After mating the two surfaces of the parts with a coincident mate I cannot then position the smaller part from the centre of its body relative to any of the edges of the larger part.

I have defed planes that intersect the centre of the smaller part and added distance mates between them and the edge of the larger part but this does not work.

I have also defined a point that intersect the centre of the mating face of the smaller part and added distance mates to the edge of the larger part but this does not work either.

In both cases i get the error message "Both of the selected components are fixed or fully defined, so any mates created between them will be ignored".

I have attached a simple demonstartion of the problem. I'm using SolidWorks 2008 SP3.1 on Windows Vista Home Premium SP1. Am I doing something wrong or is this a bug?