Question : Must Use An Updateable Query

I need to write an update query but I keep getting an error.  I need the query to update [tbl_A].[field1] from this subquery's field called [field1]:
(SELECT tbl_B.Cust_ID, Min(tbl_B.field) as field1 FROM tbl_B GROUP BY tbl_B.Cust_ID) AS My_Subquery

My_Subquery and tbl_A join on field [Cust_ID].

Answer : Must Use An Updateable Query

An aggregate query (with Min or Group By) is not updateable. You will need to redesign the query to make it updateable. What are you trying to accomplish with the join?