How to link two tablices from different datasets into one List?

I am developing an RDL with 2008 R2.  I was able to create an RDL with two matrices and two datasets.  Each matrix uses a separate dataset.  Now I need to combine these two matrices into one List.  Format is simple; it should be Matrix A, followed by Matrix B.  And then repeat in this list on every control_number field.  The control_number field from Matrix B links to the Incident_Control_Number from Matrix A.  I was able to develop a separate table for testing with expression:

=Lookup(Fields!control_number.Value,Fields!Incident_Control_Number.Value,
Fields!Incident_Control_Number.Value,"Matrix A")

This correctly shows the Incident_Control_Number.  But when I try to use this same expression as one of the parameters for the second dataset/stored proc, I get the error:

The expression used for the parameter '@control_number' in the dataset '@control_number' refers to a field.  Fields cannot be used in query parameter expressions.

Ryan D