Field on subform won't update

[Phill]

I have a form with a subform (header/detail), the subform
is a datasheet (not a continous form). The main form has
a button that does a lookup and puts that value in one of
the subform's fields. The value displays fine but it is
not being written to the table. Here is my code:

strItemID = Me.fsubDetail!ITEM_ID_TO_SHP
Me.fsubDetail!txtBinLocation = GetAllBINsForPart(strItemID)

I've tried setting the focus to different controls and
used the Docmd.Runcommand AccmdSaveRecord, same results.
Does anyone have any ideas? Thanks.