there's 2 problems i see with this page:
1) Lines 158 - 199 are duplicate code chunks of the WA DataAssist Pre-Select Relational Table code that are used to preselect the checkboxes, there should only be one.
2) In the manage relation table behavior, you have set the master key to use the WADA_Insert_aaproducts session variable, that session is only available on the insert page, not the update page.
on the update page, you need to set the master key to use the
same WADAUpdateRecordID form element that is used for the update record behavior.