In version 5.7, we extended the scope of our new Key Fields functionality to cover more mapping areas within Importacular. Unfortunately, within the Additional Addressee/Salutation mapping we did not place a conditional value on the Add/Sal (Editable Text) field. This means that Importacular in now expecting you to populate that field, even if you have populated the 'Add/Sal (Template or Id)' field.
A fix will be in place for version 5.8, but in the meantime there is a workaround.
Firstly identify or create a column/Source field in your Data Source that contains no values. Just a Source Field Name. It doesn't matter what the Field is or what it is called, just as long as the contents of that field is empty.
Next, once you have added the update Data Source and selected the relevant Template, select that Source Field in the Add/Sal (Editable Text) Source Field Name dropdown menu.
Once you have done that, go to that field's Settings.
In the field's Settings, de-select the 'Only Update Values For...' options for New Constituents and Existing Constituents.
Then Save Mapping, Save your template and complete your Import.
This workaround will address the Key Fields requirements to have that field populated, but will skip over the field to the Add/Sal (Template or Id) and ensure that is populated instead.