Yeah looks like there is a bug in Carrara where it looks for just two shaders at the top of the tree. It even gives the same message when you have a built-in top level shader that isn't Layer List or Multichannel. I'll have to report that one to Charles and Co. Just hit OK on the force drop and it should work fine.

Thanks,
Eric Winemiller
Digital Carvers Guild
Plug-ins for Carrara
http://digitalcarversguild.com

Eric Winemiller
Digital Carvers Guild
Carrara and LightWave plug-ins