If you are updating your OnePager report, you may see a warning message that states:
The field Unique ID, which is serving as task unique identifier (Unique ID), contains duplicate values and so cannot be a unique identifier. The following message shows the first non-unique value that OnePager found: "Column 'Unique ID' is constrained to be unique. Value '1' is already present."
Please go back and pick a field other than Unique ID as the Unique ID.
The message looks like this:
This message typically appears when you are updating your OnePager chart with a different Microsoft Project file than the one you used to originally create it. Maybe you save off different versions of your Microsoft Project plan each week and use the latest one to update your OnePager chart. It's perfectly OK to do this, but you want to make sure that you remove references to the old file from OnePager before updating with the new file. Otherwise, you'll end up creating a multi-project timeline, which is also something that OnePager supports, but when you create a multi-project report from two copies of the same project file, you can end up with some duplication, which is what this warning is talking about.
Normally, when you update a OnePager chart with a different file, you will get a prompt like this, which alerts you to the difference in file names, and gives you the opportunity to remove the old file. On top of that, you can also check the box to Always use the open Microsoft Project file, which tells OnePager to update your chart with whatever file you have open in Microsoft Project, and to disregard any Microsoft Project files that you might have used previously:
This is your best bet if you want to continually change the source files that OnePager will use for its updates. If you dismissed this window, or it's not appearing for you, there is another option to remove the duplicate Microsoft Project file.
Prior to updating, double-check the update wizard to see how many Microsoft Project files are referenced in your report. In this case, we see that there are two. The OnePager chart was originally created with "Project X" and now we want to update it with "Project Y", but "Project X" is still being listed as a source file:
When you see two files listed where you only want to use one, click the Add/Remove button on the wizard. OnePager will pop up a separate window with a detailed listing of all of your Microsoft Project source files. Simply highlight the file(s) that you no longer need and click the Remove button. This will remove the files from the OnePager report, but it won't actually delete the files themselves from your computer.
Once you've removed the duplicate file(s) click OK to return to the update wizard. You should now only see one file listed, and will be able to proceed with your update without any further warnings.
Last Updated: December 27, 2019