Excel VBA error code during first run only - excel

Question

I have tried several methods to eliminate my VBA error but it does not help.
During the first run, there will be error code 9. Upon running again, the code works fine. I have another code with no error but does not execute the VBA code correctly the first run. Upon running the code again, it execute the VBA code correctly.
I have tried using F8 to debug the problem, i have tried looping.
Sub TXNFont()
Dim Firstrow As Long
Dim Lastrow As Long
Dim Lrow As Long
Dim CalcMode As Long
Dim lastColumn As Integer
Dim rng As Range
Set rng = ActiveSheet.Cells
Sheets("TXN Speed").Select
lastColumn = rng.Find(What:="*", After:=rng.Cells(1), Lookat:=xlPart, LookIn:=xlFormulas, SearchOrder:=xlByColumns, SearchDirection:=xlPrevious, MatchCase:=False).Column
With Application
CalcMode = .Calculation
.Calculation = xlCalculationManual
End With
Sheets("TXN Speed").Select
Cells.Select
With ActiveSheet
.Select
Firstrow = .UsedRange.Cells(1).Row
Lastrow = .UsedRange.Rows(.UsedRange.Rows.Count).Row
For Lrow = Lastrow To Firstrow Step -1
With .Cells(Lrow, lastColumn)
If Not IsError(.Value) Then
If .Value > 3500 Then .EntireRow.Font.Color = RGB(255, 0, 0)
End If
End With
Next Lrow
End With
With Application
.Calculation = CalcMode
End With
Sheets("TXN Speed").Select
With ActiveSheet
.Select
Range("A1:A5").EntireRow.Font.Color = RGB(0, 0, 0)
End With
End Sub
Sub NetFont()
Dim Firstrow As Long
Dim Lastrow As Long
Dim Lrow As Long
Dim CalcMode As Long
Dim lastColumn As Integer
Dim rng As Range
Set rng = ActiveSheet.Cells
With Sheets("Network").Select
Cells.Select
With Selection.Font
.ThemeColor = xlThemeColorLight1
.TintAndShade = 0
End With
lastColumn = rng.Find(What:="*", After:=rng.Cells(1), Lookat:=xlPart, LookIn:=xlFormulas, SearchOrder:=xlByColumns, SearchDirection:=xlPrevious, MatchCase:=False).Column
Cells.Select
Cells.Select
With ActiveSheet
.Select
Firstrow = .UsedRange.Cells(1).Row
Lastrow = .UsedRange.Rows(.UsedRange.Rows.Count).Row
For Lrow = Lastrow To Firstrow Step -1
With .Cells(Lrow, lastColumn)
If Not IsError(.Value) Then
If .Value < 10 Then .EntireRow.Font.Color = RGB(255, 0, 0)
End If
End With
Next Lrow
End With
With Application
.Calculation = CalcMode
End With
Sheets("Network").Select
With ActiveSheet
.Select
Range("A1:A5").EntireRow.Font.Color = RGB(0, 0, 0)
End With
End With
End Sub
Sub TXNFont() will have error during first run, but will execute the code with no issue if I hit run again.
Sub NetFont() will execute the coding with error during first run, but will execute the code correctly if I hit run again.
These codes were link to another VBA code which was running fine with no issue. I hope that the codes I made run smoothly with no error during their first run. Thanks in advance people!