I have previously created migration jobs that successfully updated custom field, using the IFS instructions for handling Custom fields. This time, I am receiving an error that I don’t understand: 

it may be a clue that when I open my migration spreadsheet and Connect, it does not prompt me to Open in a New Sheet like normal.  I have compared this migration job to another one that I have created to update a custom field successfully and see no difference. 

Has anyone else seen this and know how to correct this? 

Thanks