VBA program to color all cells that have a value - excel

Question

I just started teaching myself VBA so thanks in advance. Why is this giving me an error? The code searches for the column of dates that are in the future. Then searches in that column for any cells that have a value and colors them yellow.
Thanks!
Sub Macro1()
Dim cell As Range
Dim cell2 As Range
Dim ColumnN As Long
For Each cell In Range("I2:ZZ2")
If cell.Value > Now() Then
'
ColumnN = cell.Column
ColumnL = ConvertToLetter(ColumnN)
MsgBox ColumnL & cell.Row
For Each cell2 In Range("ColumnL:ColumnL")
If Not cell2 Is Empty Then
cell2.Interior.ColorIndex = 6
End If
Next cell2
End If
End Sub()
Function ConvertToLetter(lngCol As Long) As String
Dim vArr
vArr = Split(Cells(1, lngCol).Address(True, False), "$")
ConvertToLetter = vArr(0)
End Function

Answer 1

You were almost there!
There's two main problems to fix:
replace:
For Each cell2 In Range("ColumnL:ColumnL")
with
For Each cell2 In Range(ColumnL & ":" & ColumnL)
and
If Not cell2 Is Empty Then
with
If Not IsEmpty(cell2) Then
This should result in the following:
Sub Macro1()
Dim cell As Range
Dim cell2 As Range
Dim ColumnN As Long
Dim ColumnL As String
For Each cell In Range("I2:ZZ2")
If cell.Value > Now() Then
ColumnN = cell.Column
ColumnL = ConvertToLetter(ColumnN)
MsgBox ColumnL & cell.Row
For Each cell2 In Range(ColumnL & ":" & ColumnL)
If Not IsEmpty(cell2) Then
cell2.Interior.ColorIndex = 6
End If
Next cell2
End If
Next cell
End Sub
Function ConvertToLetter(lngCol As Long) As String
Dim vArr
vArr = Split(Cells(1, lngCol).Address(True, False), "$")
ConvertToLetter = vArr(0)
End Function
Although it is a little inefficient it gets the job done!

Answer 2

To check if a cell is empty, you need to switch the order of how that's done. Switch your If Not statement to If Not IsEmpty(cell2) Then.
Also, it is highly recommended not to name your variables cell, because this is a close to some "special words" (I forget the technical term) Excel uses. I always just use cel instead.
Sub test()
Dim cel As Range
Dim cel2 As Range
Dim ColumnN As Long
For Each cel In Range("I2:ZZ2")
If cel.Value > Now() Then
ColumnN = cel.Column
' ColumnL = ConvertToLetter(ColumnN)
' MsgBox ColumnL & cell.Row
If Not IsEmpty(cel) Then
cel.Interior.ColorIndex = 6
End If
End If
Next cel
End Sub
Edit: If you notice, I also tweaked your cell2 range. This removed the need to run another macro (which can be a cause of issues sometimes), so you only need the column Number.
Edit2: I removed the "ColumnL" range selection - what is that for? I can add it back in, but wasn't sure why you'd loop through I:ZZ columns, but only have the highlighting in column N.
Edit2:
I tweaked the code, now it's much shorter and should run a bit faster:
Sub Macro2()
Dim cel As Range, rng As Range
Dim lastCol As Long
Application.ScreenUpdating = False
lastCol = Cells(2, 9).End(xlToRight).Column ' Note, this assumes there are NO gaps in the columns from I:ZZ
'lastCol = cells(2,16384).End(xltoleft).column ' use this instead, if there are gaps in I2:ZZ2
Set rng = Range(Cells(2, 9), Cells(2, lastCol))
For Each cel In rng
If cel.Value > Now() Then
cel.Interior.ColorIndex = 6
End If
Next cel
Application.ScreenUpdating = True
End Sub