Message Box Fails to Appear

I am writing code to have a message box appear when data from two spreadsheets do not match. When I run the code the first time the message box appears. If I run the macro a second time, the message box will not appear. If I modify the code and run the macro, the message box will appear, but will not appear the second time, or thereafter. I don't get any error messages and the code runs correctly. The only thing not working is the message box failing to appear on the screen. I have run a test in a blank worksheet and the message box appears everytime I run the macro.

Here is the code:

Sub ValidateHours()
If Range("MTD_Hours") <> 0 Then Call ErrorMsg
If Range("YTD_Hours") <> 0 Then Call ErrorMsg
End Sub

Sub ErrorMsg()
'
'Displays a message that the report does not equal the hours in the STATS.
'
'
    Sheets("Report").Select
    Range("A69").Select
    MsgBox "The actual hours do not balance to the STATS report."
    
    
End Sub