I have a few parts that I have inserted into the main assembly, and I now want to make them part of one of the sub assemblies. I have the option to 'form a new sub assembly' when I select one or more of the parts, but when I select one of the parts and the sub assembly I want to add them to I get the error 'All components must share the same common parent'. I actually don't want to form a new sub assembly, I just want to add the parts to the sub assembly that is already there, while keeping the mates I made in the main assembly. If I open the sub assembly I can then insert the parts and mate them all up again but I thought there must be a way to do this from the main assembly.

Does anyone know how I can do this?