Text Box Message Not Displaying

Hi I wonder if someone can help me with this.

I have an access database in which there are tab controls to collect text written about a subject. My problem is that there are nine tabs all with the exact same code behind them, but obviously varying object names for the relevant text boxes. Four of them work as expected and five don't.

The following code has been used to display a popup if the user types too much text and it works for the Environ_Plan text box:

Private Sub txtENVIRON_PLAN_Change()
Dim strMessage As String, varLen As Variant

varLen = Nz(Len(Me.txtENVIRON_PLAN.Text), 0)
If varLen > 250 Then

strMessage = "You have exceeded the limit of this field by " & (varLen - 250) & " characters." & vbNewLine
strMessage = strMessage & "The maximum allowable length is " & 250 & " characters."
MsgBox strMessage, vbOKOnly + vbExclamation

End If
End Sub

(note that if the user types 251 characters an error message appears on the screen to say they have exceeded the number of characters allowed for that box and they cannot type any more text.)

The following text is used for the exact same outcome in Health but it does not work:

Private Sub txtHEALTH_PLAN_Change()
Dim strMessage As String, varLen As Variant

varLen = Nz(Len(Me.txtHEALTH_PLAN.Text), 0)
If varLen > 250 Then

strMessage = "You have exceeded the limit of this field by " & (varLen - 250) & " characters." & vbNewLine
strMessage = strMessage & "The maximum allowable length is " & 250 & " characters."
MsgBox strMessage, vbOKOnly + vbExclamation

End If
End Sub

(In this case the cursor stops and the user cannot type any more text but no message appears to say why the cursor has stopped.)

I have double checked the actual variables in the Access database and they are set to the exact same values.

I am using Access 2002 on Windows XP Professional.

thank you in anticipation.

Ouma