Using geometry from one part as a reference to create geometry on another in an Assembly

Hi,

I have an assembly with a few parts. I want to use some of the geometry from one of the parts as reference (create planes etc.) and create new geometry in another part. When I try to do that I get a message saying “the component being edited is locked. You can edit the component but can’t create an external reference…”  Although I am fine with this message I can’t do anything because the dialog box keeps on flashing :-(

Thank you,

SolidworksAssemblies