Using skew angles larger than 45 degrees
It was not possible to generate a cylinder or cone with one end truncated at an angle larger than 45 degrees.
The idea behind Cone Layout originally was to create exhaust-pipes for motorcycles. In order to be able to "bend" the exhaust-pipe around the engine, Cone Layout could skew the sides of the cones. However, for an exhaust-pipe it is unthinkable to create a bend of more than 90 degrees (thus having two cones with a skew angle of 45 degrees).
This is not a limit of the calculation algorithm, it was just a hard-coded limition in the dimensions entry window to catch human mistakes. Now that the program seems the be used for many more applications than I had ever forseen (from paper card modeling to making biomechanical devices for disabled people), it might be a good idea to remove the 45 degree limitation, and only have it limited by the actual geometry of the cone.
Solution / workaround
This problem is fixed in Cone Layout version 1.3 by removing the angle limits from the dimensions window. Please download this new version if you are experiencing the problem above.