Source Custom Field Value onto Employee list field

Hello,

In a workflow, I am trying to source an employee name that is stored on a custom text field into another custom field that is a list field based on the employee list. I have been trying to accomplish this by sourcing the custom field via a formula because the two field types don't match. I am getting the workflow to activate "Before Record Submit". I keep getting the following error below even though the names are an exact match. Does anyone know a way around this error? Both custom fields are on the same record, which is a requisition