Message when change info in a form

[BarbaraF]

I have a form with a listbox where the record source is 2
fields in a table. Double click on an entry and you get
another form where you can make changes to the data.
There is a button to exit the form. When you try to exit
you get " The record has been changed by aonther user
since you started editing it. If you save the record you
will overwrite the changes the other user has made. I
take the option "Drop Changes". Any ideas on why I get
this?? Thanks!