Client user see option for Gantt Chart under Reports tab but can not see the chart

Client user see option for Gantt Chart under Reports tab but can not see the chart

As the Project user I can see the Gantt Chart report but the client user on the same project only see the option for Gantt Chart on the Reports TAB but clciking it does nothing yieding no report. This client user has been assigned to the external projects tasks as a user and can view Task lists etc