3823239 - Error: "Field 'first_name ' contained one or more invalid characters. The record was processed but not imported."

When uploading employee data via the SFTP using record 305 I am getting the following error message: 
Error: "Field 'first_name ' contained one or more invalid characters. The record was processed but not imported."
I am importing users with names containing some of the following characters: " ç, â, ä, à, é, è, ê, ë, î, ï, ô, ö ù, û, ü"

Employee data are imported with invalid characters and we are getting following error on the Employee import: Error: "Field 'first_name ' contained one or more invalid characters. The record was processed but not imported." , KBA , CON-CA-TLS-IEM-JOB , Scheduled Jobs , CON-CA-TLS-IEM , Import / Extract Monitor , Problem