Error Message when using External Data spreadsheet

Summary:

error message when adding data to a column on External Data. It says that they don't recognise the Person Number or Assignement numbers even though they do exist. also I am able to load external data with the manual option...

Content (required):

Hello experts,

I am trying to load the columns of the External Data table via spreadhsheet. However, when I do this I get an error message saying they don't recognise the person number saying it does not exist: (sorry it's in french)

However, when i go into person manager i can see that it does in fact exist: