Hi Tony,
Can you please tell us more about what process you are trying?
The best way is to create only Merchandise Category (WG21) first. Here when you define a MC, you do not need to attach any reference article.
Once you are done with creation of merchandise category, using WG22, you can click on MC Reference article button to create a reference article for your selected merchandise category.
Let me know if you need more help.
Regards,
Amit