If you see an Exception message such as "Error reported from RE on saving the record from the area map "Constit". The reported error was: Required Field Missing: Constituent Code" this means that your mapping template does not include a mapping for a field that is required.
In the sample provided, this means that there is a constituent being created that does not have a Constituent Code. To resolve this, check the Constituent tab in your mapping template and ensure that you have a Constituent Code mapped. If you are working with a paid destination that allows you to create secondary Constituents (such as the destinations for Individual Relationships, Organisation Relationships, Solicitors/Canvassers or Tributes), you may need to add a Constituent Code (or other required field) for those areas. You can read more about secondary Constituent mappings here.
For additional information, you may also refer to the Blackbaud knowledgebase article on the same topic.