I am a little confused... What is the name of the control that the account number is in? FSS? If you are referencing a control you would use a period (Me.FSS). If there is a data field called FSS in the underlying data then you would use Me!FSS.
I suspect the problem is that Me!FSS is the underlying data that is NOT changing. It will only change when you have saved the data. I think you probably want to change it to Me.FSS which probably references the text box.