Events Not Triggering

Access front end, SQL Server backend.
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I have a continuous subform (part of a tab control on a main form) whose name and sourceobject are both "sbfCannulae". There are about 10 fields on the subform, and all are bound to fields in a table. The primary key of this table must be generated by combining two other fields, which must happen just before the record is saved. (I know calculated data should not usually be saved in tables, but trust me. In this case it is necessary.)

Right now the user COULD enter data into the primary key-bound textbox, but since the user is me, I make sure not to do that.

When I enter data into all fields except the primary key, I get an error because the primary key cannot contains nulls...of course.

I use the following code to tell me when an event has been triggered.

Code associated with sbfCannulae:
Option Compare Database

Private Sub Form_Activate()
MsgBox "cann activate"
End Sub

Private Sub Form_BeforeInsert(Cancel As Integer)
MsgBox "cann before insert"
End Sub

Private Sub Form_BeforeUpdate(Cancel As Integer)
MsgBox "cann before update"
End Sub

Private Sub Form_Current()
MsgBox "cann current"
End Sub

Private Sub Form_Dirty(Cancel As Integer)
MsgBox "cann dirty"

End Sub

When I enter data into a new record, the Dirty event is triggered, but I cannot for the life of me figure out how to trigger any of the other events. No combination of values and nulls in any fields, clicking in other tabs, clicking to other records, or using the navigation buttons will ever trigger any events but Dirty.

The only msgbox I ever get is the one giving delivering the SQL error about the primary keys not taking null values.

What am I doing wrong?

-Matt