I have a sketched a quite complex face (text created by using splines) and want to extrude this.
I get the error Extrusion failed.
I think it would be nice if you included a reason for the failure.
Question is what to do now, because I really need this extrusion.
Another issue I experienced is that I use the spline tool (fit mode) and often when I come back after closing S3D, parts are changes into splines in control mode with many control points.
This makes it very difficult to keep the text as simple as possible.