Sometimes when I open an assembly I will not be able to select a specific part within that assembly. I will not be able to select an edge, face, plane, or vertices on that specific part. This part may be in a sub assembly or by itself. The rest of the model will behave normally. I can see the part, it just acts as if it is not there. If I open up that part file and leave it open the assembly file will begin to work. I have tried setting all of the parts to resolve, or changing their displays but nothing seems to help. I have the same problem when I make a drawing of these assemblies. I can see the part but I can not select any edges, or vertices for dimensioning them untill I open up the part file. It is not consistent which part will not work within these assemblies and most of these assemblies are quite small, less then 10 parts including parts in sub-assemblies. Any suggestions on what I should do to prevent this.