In latest Autodesk Softimage, you could have this error :
misss_call_shader: Unexpected state->type case.
If you have it, the shader is style working, but much slower...
So, here is the fix (version 1.4.2) : Dispersive GEM Shader 1.4.2
I don't have anymore errors and it is really faster !
To know more about the shader, read the previous posts : Dispersive GEM Shader 1.4.1 and the Original GEM dispertion shader compound version 1.0
Enjoy it !