The MPCPro Output Variable Dynamo can be used for both Controlled and Constraint variables.
If you use the browse button to configure an MPCPro Output variable dynamo you must edit the Node.Module/FB_Name field on the Dynamo Properties dialog and remove the parameter and field names that are added as a result of the browse. This field must contain only node, module, and function block name. Parameter and field names are not allowed. For example if the field is populated with Node1.MyModule/MPC-Pro1/Proc_OUT.F_CV after the browse, edit it to Node1.MyModule/MPC-Pro1.
You must include the actual output variable name (CV or AV) in the Parameter Description field on the Dynamo Properties dialog.