Could someone help me understand what I'm missing here...

I have a Userform with a TextBox (tbT_Code1) and I'm trying to trap
for non-integer entries OR integer entries outside established
limits (iRetCodeMin < value < iRetCodeMax).

My code (with iRetcode1, iRetCodeMin & iRetCodeMax all declared as
integers) is as follows:

Private Sub tbT_Code1_Change()
If tbT_Code1 <> "" Then
On Error Resume Next ' Trap a non-integer entry
iRetCode1 = tbT_Code1.Value
If iRetCode1 > iRetCodeMax Or iRetCode1 < iRetCodeMin Then
MsgBox "You have entered an invalid 'Return Code'..." &
Chr$(10) & Chr$(10) _
& "Please enter a valid code from the list above."
tbT_Code1 = ""
' Exit Sub ' Force the error trap to reset
Else
sReason1 = Application.WorksheetFunction.VLookup _
(iRetCode1, Range("RetCode_Lookup"), 2, False)
tbT_Reason1 = sReason1
End If
End If
End Sub

The trap & test seems to work as desired if a non-integer or an out
of range value is entered INITIALLY (displays the message then
clears the offending value).

Problem I'm having is if a "valid" code is entered and then the user
highlights/edits the code to an "invalid" code neither the "Error
Trap" nor the Vlookup are activated. Shouldn't the "changed" value
re-run the Sub tbT_Code1_Change code?