Queries :: Update Table With The Value Of Union Query

I have a table with a field I want to update with the value of a Union Query

The field I want to update is Yes/No format and I can update using 0 or -1 OK.

However, when I link in the union query (and check that I only have 1 update result which is either 0 or -1) I get an error message saying that Operation must use an updatable query.

I guess this is referring to the Union Query (although I am trying to update the table and not the query.

In short - I want to update a table based on the value of a union query.

Code:
UPDATE tbl_StaMe_NGR_Subscription INNER JOIN qry_QDF_QRYDEF1 ON (tbl_StaMe_NGR_Subscription.EmailType = qry_QDF_QRYDEF1.Type) AND (tbl_StaMe_NGR_Subscription.AgentEmail = qry_QDF_QRYDEF1.Email)

Code:
SET tbl_StaMe_NGR_Subscription.Subscribed = [Subscription];