Displaying an Error Message

[mapat]

Hello,

I have "txtBoxA" (where the user types in a number) and "txtBoxB" (which is updated automatically) on a form. I would like to display a message (Box message) that would not allow the user to go on when: "txtBoxB" gets updated and this updated value is greater than the value on "txtBoxA" (typed by the user in the beginning)

How would I achieve this??

Thank you very much

 

[missinglinq]

Exactly how is "txtBoxB" updated automatically?

 

[mapat]

"txtBoxB" is basically a counter. It adds the values (that I type in) on other text boxes.
The control source for "txtBoxB" is: = txtBoxM + txtBoxN + txtBoxO + ..... and so on.

When "txtBoxB" reaches the value of "txtBoxA" I want to display the message

thank you