Run Time Error 13 - Mismatch on Date - vba

Question

avid reader, first time poster here. I have a Macro that I obtained from the internet for the most part, then made some adjustments. It's purpose is to color code cells that have passed a certain duration. It was working fine earlier, but now I am getting an error on it for a "Type Mismatch". The line that reads "This is where the error is" is where I am getting the mismatch. I am puzzled because it was working fine earlier. I am not a seasoned programmer by any means, but I just try to troubleshoot things. I have looked all over the net and cant find a specific answer to my question.
In addition, if any of you are willing, I would appreciate your advice on how to make this code run ONLY at startup of the workbook and NOT periodically as it is set up to do so now.This code is not placed in a worksheet, but in a Module.I mention this because I am not sure how much of a practical difference it can make any help is appreciated, thanks!
Public TimeToRun As Date
Sub Auto_Open()
Call ScheduleCompareTime
End Sub
Sub ScheduleCompareTime()
TimeToRun = Now + TimeValue("00:00:10")
Application.OnTime TimeToRun, "CompareTimeStamp"
End Sub
Sub CompareTimeStamp()
Dim rgTimeStamp As Range
Dim rdTimeStamp As Range
Dim i As Long
Dim j As Long
Dim MyNow As Date
Dim TimeStamp As Date, TimeStampp As Date
Set rgTimeStamp = Range("c1:c500")
Set rdTimeStamp = Range("H1:h500")
For i = 1 To rgTimeStamp.Rows.Count
If Not rgTimeStamp.Cells(i, 1) < 1 Then 'don't run for an empty cell
MyNow = CDate(Now - TimeSerial(0, 0, 0)) 'time instantly
TimeStamp = CDate(rgTimeStamp.Cells(i, 1)) 'THIS IS WHERE THE ERROR IS!!
If TimeStamp < MyNow Then 'if it's old at all
rgTimeStamp.Cells(i, 1).Interior.ColorIndex = 3 'make fill colour red
End If
End If
Next
For j = 1 To rdTimeStamp.Rows.Count
If Not rdTimeStamp.Cells(j, 1) < 1 Then
MyNow = CDate(Now - TimeSerial(0, 0, 0))
TimeStampp = CDate(rdTimeStamp.Cells(j, 1))
If TimeStampp < MyNow Then
rdTimeStamp.Cells(j, 1).Interior.ColorIndex = 3
End If
End If 'closes If Not
Next
Call ScheduleCompareTime 'begins the scheduler again
End Sub
Sub auto_close() 'turn the scheduler off so you can close workbook
Application.OnTime TimeToRun, "CompareTimeStamp", , False
End Sub

Answer 1

You probably have data in one or more cells that Excel cannot convert to a date. You can get around this by adding some simple checking such as this:
'.... beginning of your code
If Not rgTimeStamp.Cells(i, 1) < 1 Then 'don't run for an empty cell
MyNow = CDate(Now - TimeSerial(0, 0, 0)) 'time instantly
If IsDate(rgTimeStamp.Cells(i, 1)) = False Then
MsgBox "Invalid date found in cell " & rgTimeStamp.Cells(i, 1).Address(False, False)
Exit Sub
End If
TimeStamp = CDate(rgTimeStamp.Cells(i, 1)) 'THIS IS WHERE THE ERROR IS!!
If TimeStamp < MyNow Then 'if it's old at all
rgTimeStamp.Cells(i, 1).Interior.ColorIndex = 3 'make fill colour red
End If
End If
'... rest of your code
If you only want the code to run at startup then change Sub Auto_Open to this:
Sub Auto_Open()
Call CompareTimeStamp
End Sub