The "other user" is yourself on the form. This error is a very common problem when accessing records in two different ways and trying to edit them. It doesn't cause a problem with the Form After Update because the record edit on the form is completed before the code is run. If you use the control AfterUpdate the record is still dirty when you run the code and Access detects the conflict.
The actual mistake is loading a bound form, starting an edit on a record then attempting to edit the record in the recordset. It is bad design and wrong thinking.