>I provide users the facility to modify reports in a runtime version of VFP6 using a command -
>MODIFY REPORT MyReport
>How can I activate the Report Controls Toolbar when this happens?
>SYS(1500, '_mvi_toolb', '_mview') does not work

The only way i can think of is to get it open automatically with help of RESOURCE file. Make sure that SET RESOURCE is ON and resource file has required toolbar settings.