I'm sorry by the mistake, but the reply of yuv is not correct. It's not a limitation of RailClone Lite.
You must increase the 'Limits' values in the General rollout. These parameters define a maximum size of the RailClone object (in number of segments and millions of faces), to avoid creating huge meshes when using very long splines of large segments.
You can also set the 'Display as boxes' toggle (in General rollout as well), to improve the viewport performance. In this case, the Limit values are applied only while rendering.
In RailClone Pro 1.1 beta, we have improved this behaviour. The 'Box' mode is automatic, and we use the VRay engine to create instances of the geometry, allowing to build huge objects with minimal resources (similar to Forest).