If you are attempting to build a Gantt chart from multiple Microsoft Project files, OnePager sometimes gives you a warning that states:
Sorry, we have detected duplicate Project Summary Tasks in your Microsoft Project plans. We recommend you check the Project Summary Task of each of your Microsoft Project plans to remove duplicates before continuing with import
The message looks like this:
In older versions of OnePager, the message has different wording:
Found a task that could not be imported.
Object reference not set to an instance of an object.
The older message looks like this:
This message appears because two or more of your Microsoft Project plans have the same name. The filenames (*.mpp) are probably different, the the project names themselves may not be. We often see people copy one project plan to create another one. People always remember to change the filenames, but often forget to change the Project Summary Task, because Microsoft Project doesn't usually make it visible.
In this example, we started out with a project plan called "Project A". After a while, we needed to build a second project plan, so made a copy of "Project A" and renamed the file to "Project B". However, the Project Summary Task is still carried over from the original project file, and still reads "Project A."
To double-check your project summary task, open one of your Microsoft Project Plans, go to the Format tab, and check the Project Summary Task box. The project summary task will then show up in the very top row of your plan--line 0:
OnePager can build a Gantt chart from as many different Microsoft Project plans as you need, but each project plan does need to have a unique project summary task. In most cases, simply correcting the duplicate project summary task name will address this issue, and will allow you to proceed with building a multi-project timeline or Gantt chart.