Null reference exception (maybe too much nodes ?)

Hi,

this is a new topic about a Null Reference exception I had yesterday with my shader.
It is just a little modification of the custom lighting shader from the 0.17 package examples. the other part is an edge detect outline base on an UDK shader I found on the Eat3D forum. (This part of the shader is not yet fonctionnal because of the Scene Depth node. I think it is actually in development.)

For the errors, when I cut some splines or delete one texture2D or color node, the ShaderForge window completely freeze (Not Unity) and the node box disappears.
(I can not reproduce the problem. Strange.)

PS : Is there a zoom feature somewhere ? A screenshot button could be a good feature too.