dot error indexing message in Spectrum Analyzer

Hi

Suddenly today appears the "dot indexing is not supported for variables of this type" error message when I try to expand the spectrum analyzer inputs beyoind 3 in Simulink model .Now the the only way I have to place a SA with more than 3 inputs is copy and paste from models already created. Should be a very simple thing (maybe I´ve changed some config not on porpouse) but I don´realize what could be. Could anybody shed light on this? Thanks