HI HomerJ,
As per the administrator guide, the default maximum number of concurrent projects is 6. By adding the following parameter to the site configuration tab within the site administration section, then the maximum number can be raised to include more projects, be warned that this may affect system performance by increasing this number above the default:

PROJECT_ SELECTION_ MAX_PROJECTS
By default, cross-project graphs can include up to six projects.
This parameter enables you to set a different number of maximum projects that cross-project graphs can include. Increasing the number of projects may reduce the system's performance.
For more information on cross-project graphs, refer to the HP Application Lifecycle Management User Guide.

You will need to stop and restart the services for this parameter change to take effect and be applied.

I hope that helps,
Dan