Just as the title says. Whenever I try to extrude this spline, it simply disappears. However, I still have the option to move this invisible object around. Like maybe it did extrude the spline, but it is just invisible. Weird.
Here is an image of my spline that needs to extrude:
http://i.imgur.com/UIo6oZQ.jpg
Replies
This is only a general way of doing it. You could also use shapemerges and other methods.
Good, this works also. The other solution was probably turning invisible because of welding problems.