Tim,

I found the problem - - -

The application has 3 queries - all the queries have a datasource assigned (which is not
necessary - there are no parameters in the SQL)

The buttons [Derived Table Query] & [No Derived Table Query] both execute a query that
have the SQL assigned at design time.  Both work OK.

The button [Query - Swap Datasource] has the SQL assigned at run time.  Firstly it assigns
the SQL WITHOUT the Derived Table.  Works OK.  Then it assigns the SQL WITH the Derived
Table.  Does not work.

Everything works OK if the DataSource is not assigned to the query.

It is rather obscure set of circumstances.

Hope this makes a bit more sense.

Richard Harding