This probably means you have a circular reference, this can happen when part A depends on part B for some of its definition, but part B depends on part for his. Something has to give.
It's easy to make a situation where you get into this, it can be helpful to use a skeleton part and use that to drive your individual parts from, as you're links will mostly (if not all) point and go through just one model, your skeleton. Use sketches and planes and lines to define key functional areas.
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