Please Help! C# DAL Method Updating Multiple Tables

[ DAL Method Update() ]

Please help I have two tables, one form. My two tables are tblAsset and tblSites.

I've made a form of the tblasset and I would like to add a field in from the tblSites "tbllookupSites". I've been adding this code to update\edit a record, I have added this code in the "before record updated" sections.

set dal_table=dal.Table("tbllookupsites")
dal_table.SiteNotes=values("SiteNotes")
dal_table.Update()

This code doesnt work? Where am I going wrong.