Hi Terry,
The issue caused because of the absence of Base Theme in the respective Application Module as shown below.

You can reference the Base Theme from the OutSystemsUIWeb module suing the Manage Dependencies as shown below

And also add the screen layout (e.g. Common\LayoutTopMenu) in the respective POC screen for more structuring of the screen.

Please refer to the attached updated .oml file
Hope this helps you!
Kind regards,
Benjith Sam