I am working on two assemblies for a fixture that holds parts during a milling operation. A component called the "base plate" is common to both assemblies. In the first assembly, several external references to other components are used to define locations of threaded mounting holes in the base plate. Additional mounting holes are needed in the base plate for mounting other components in the second assembly, so I wanted to "trace" one of these components onto the base plate. To do this, in the second assembly I selected the base plate and clicked Edit Component. I then opened a new sketch on the top plane of the base plate. Next, I selected the edges of the component that I wanted to trace and then clicked Convert. A message about not being able to create external references popped up and the Convert operation failed. First, how can I get around this? Second, how does converting sketch create an external reference?