As you are drawing a polygon, you may inadvertently draw an object that cannot be "closed" (completed). When this happens, the program does not accept the double-click action when you attempt to complete the object and the area takeoff object usually flashes yellow with a bold red border. You need to backup by pressing the ESC key until you get to a point where you have not crossed lines to create that "uncloseable" area.
In the example below, we crossed segment lines, effectively creating two areas, which is not allowed.
This often occurs when you try to draw the last segment by placing the final point at your starting point - the two points are likely off a bit and your line crosses - that is why it is best to double-click at the point that starts your final segment and let the program draw that last segment for you.
This can also happen when you are drawing a complex polygonal shape - it may be easier to break up a very complex area into smaller takeoff objects, although you will increase your perimeter Results a little.
Once you back-up to the point where you crossed lines, examine what you are drawing to ensure you can complete the object, or break the takeoff into multiple, separate objects.
Polygon Areas with Curved Segments