Imported contour lines from CAD not turning into surface

Dear all,
I have these contour lines (converted from shapefile to CAD file in ArcGis software) imported to Sketchup Pro.

I want to make a terrain from these , so I used the From contours tool in Sandbox toolbar, but it gives me this error message!

As you see, I selected the lines before clicking on the tool, so I do not know why I get this message. Any idea if there is something wrong with my contours or am I doing something wrong? Thanks.

Looks like you selected the group that contains the contours rather than the contours themselves.
Double click to open for editing, or right click open for edit, or even explode if you want.
Then select the raw geometry and use the extension.
The blue bounding box needs to turn gray before you are in edit mode.