Follow these steps:

1. Click on Planes > Show/hide planes. Select the bars in the area where the frame in question stands.
2. Click on Planes > Ungroup. Choose the orientation of the plane coinciding with that of the frame.
3. Left click on the plane containing the frame to select it (be careful not to select another) and right click to exit.
4. Answer Yes to confirm the selected plane is to be ungrouped.