Armored Wing,

In the future please use Code tags (and not Quote tags) to surround code (see Forum Rules link in my sig for how).
As to your question, its becuase you're trying to overwrite existing data validation without clearing the old stuff. Added a .Delete line to your code, give it a try:
Sub CheckBox_Financial_Statement_Annual_Click()
    
    Const PassVar As String = "test"
    
    ActiveSheet.Unprotect PassVar
    
    If ActiveSheet.CheckBoxes(Application.Caller).Value = xlOn Then
        ActiveSheet.Range("A70:H74").UnMerge
        ActiveSheet.Range("A70").Value = "Enter Multiple GCIF below and Select appropriate Doc Type from drop down list"
        ActiveSheet.Range("A71").Value = "Financial Statement - Annual"
        ActiveSheet.Range("B70:H70").Value = "Select Doc Type from drop down list"
        With ActiveSheet.Range("B71:H74").Validation
            .Delete
            .Add xlValidateList, , , "=$N$2:$N$99"
        End With
    Else
        ActiveSheet.Range("A70:H74").Value = Null
        ActiveSheet.Range("A70:H74").Merge (True)
        ActiveSheet.Range("A70").Value = "Comments"
    End If
    
    ActiveSheet.Range("A70:H74").Locked = False
    ActiveSheet.Protect PassVar, True, True, True
    
End Sub