Problems with assemblies

Network Blitz Hi I have a problem with an assembly. I have drawn a castor wheel,with a 80mm bolt( much like a shopping trolley),by fixing the bolt, I can rotate the wheel and castor, in all the directions that it should rotate and not in the directions that it shouldn't.. the problem comes when I insert this assembly in to another assembly (25mm square extruded box section). it refuses to rotate at all. Even if I don't constrain it to the other parts in the second assembly, and just fix the bolt. I am only using the concentic and coincident mates in the castor assembly. Another problem that I have is that if I try to contrain (coincident and concentric) the castor to the tube insert( which contrained to the box section) I get an error stating that the assembly is over constrained! but without these constraints the castor would fall off!! Oh! one more thing, Smart fasteners, AAhhhh! Am I trying to use this the wrong way? I have a 25mm square box section with two, "4mm tapped holes"(not cut extrusions) and a planel with two 4.2mm cut extrusion holes. I want to fix the panel to the box section using two, 4mm panhead screws and washers, but smart fasteners states that there are no suitable holes?? Hmmmm, I will learn this program one day, maybe? lol