Trouble deriving complex models

[evandiplacido]

I am making a 6 axis robot arm. I made the upper arm as a prototype first because it's quite complicated.

I made the lower arm next. Now I'm trying to add the upper arm into the lower arm.

Whenever I derive the upper arm, all the joints get very messed up.

 

When I "Insert into current design", it works well. The only thing I found that didn't transfer over were the motion studies, which I can easily redo. However, I need to modify it a little, which means I need to break the link.

This message box is shown:

 

With both options, it always results in the following error:

 

I think the solution would be to break the link of everything in the upper arm, however I have a thousand components in it, and I don't want them disconnected.

How do I derive or add the upper arm into my lower arm without breaking anything and also be able to modify it?

I cannot provide any files of my robot arm, but I can answer questions and share images.