@dave r said:
What is the object you're importing? Where are you importing it from? If it's really locked, it'll show a red bounding box when you select it. Right click on it and choose Unlock. Then you can open it for editing. If it is simply a blue box, it isn't locked. Just double click on it with Select or right click and choose the appropriate option--Edit Component or Edit Group.
It is a blue box. I have imported 3D Step files. I double click it an choose Edit Component. But still I can't activate the single line with the Arrow tool! I can only rotate the hole element.