Greetings,

I have a function which converts a column number reference to a letter reference. However, when I try to pass that converted column letter reference using 
Columns("E:" & myCol).Select
or 
Columns("E:" & myCol & "").Select
, I receive a "Run-time error '1004'." I've tested the function using: 

Sub Test2()
MsgBox GetColumnLetter(100)
End Sub
and it correctly displays the column letter.

Below is my macro and function:

Sub Test1()
Dim lc As Long
Dim ws As Worksheet
Set ws = ThisWorkbook.Sheets("sheet1")
lc = ws.Cells(3, ws.Columns.count).End(xlToLeft).Column
myCol = GetColumnLetter(lc)
    'Columns("E:" & myCol & "").Select
    'Columns("E:" & myCol).Select
    Selection.ClearFormats
End Sub

Function GetColumnLetter(colNum As Long) As String
    'http://stackoverflow.com/questions/16941083/use-last-column-for-a-rangeflastcolumn
    Dim vArr
    vArr = Split(Cells(1, colNum).Address(True, False), "$")
    GetColumnLetter = vArr(0)
End Function