Microsoft project management software used to plan, manage, and communicate a project schedule and other information among workgroup members, project managers, and other stakeholders.
You still have several commas in the formula.
Something else I saw only now: you use curly quotes around the text strings. You should use straight quotes in expressions/formulas. So if you use point as decimal separator:
IIf([t_En]=1, "Complete", IIf([t_En]=2, "On Schedule", IIf([t_En]=3, "Late", IIf([t_En]=4, "Future Task", "Not Applicable"))))
And if you use comma as decimal separator:
IIf([t_En]=1; "Complete"; IIf([t_En]=2; "On Schedule"; IIf([t_En]=3; "Late"; IIf([t_En]=4; "Future Task"; "Not Applicable"))))