Column Cell Count with variable in column marker, Type mismatch

Having some problems on this one, im sure its right in front of me. Can anyone help find out why this is?

Type Mismatch

Dim ColumnsInsert As Integer
Dim MyCountVar As Integer
Dim ColLetter As String
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Sub Test ()

CheckColLetter

GetCellCountsColVar

ActiveSheet.Range("" & ColLetter & "1:" & ColLetter & "" & MyCountVar & "").RemoveDuplicates Columns:=1, Header:=xlNo

End Sub
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Sub GetCellCountsColVar ()

'Errors>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
MyCountVar = Cells(ActiveSheet.Rows.Count, " & ColumnsInsert & ").End(xlUp).Row
'End Error>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
LastPlusOneVar = MyCountVar + 1

End Sub
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Sub CheckColLetter ()

Select Case ColumnsInsert
    Case "2"
      ColLetter = "B"
    Case "3"
      ColLetter = "C"
    Case "4"
      ColLetter = "D"
    Case "5"
      ColLetter = "E"
    Case "6"
      ColLetter = "F"
    Case "7"
      ColLetter = "G"
    Case "8"
      ColLetter = "H"
End Select

End Sub

wow.... the " & & " around the variable dont need to be there. not sure why though. can anyone elaborate on this?