p:IGI+ relies on Windows Direct-X9 for rendering data points on graphs, where possible using graphics hardware to improve the rendering performance. This would normally be installed as part of running the installer for the software, however if a custom install is done this step may be missed.
It is relatively easy to fix this by adding the Microsoft DirectX® 9.0c End-User Runtime which is available from the Microsoft website. Follow the installation instructions for that site. Installing this should then enable the plotting of data points on graphs.