VBA Type Mismatch Error

Change the array to Long as the border types can be expressed as such.

With arrays, a simple For instead of For Each is quicker.

I also changed the name of the array, just to not be like the command.

Then you use: Range.Borders(brder(i))

Sub Test02()
    Dim brder(1 To 5) As Long
    Dim i As Long

    brder(1) = xlEdgeTop
    brder(2) = xlEdgeBottom
    brder(3) = xlEdgeLeft
    brder(4) = xlEdgeRight
    brder(5) = xlInsideHorizontal

    For i = LBound(brder) To UBound(brder)
        With Range("'Timesheet Calculator.xlsb'!Feilds").Borders(brder(i))
            .LineStyle = xlContinuous
            .Color = -2315144
            .TintAndShade = 0
            .Weight = xlThin
        End With
    Next i

End Sub