Error in 'prova1har​dware/Unbu​ffer': All sample times must be discrete. No continuous or constant sample times are allowed.

Error in 'prova1hardware/Unbuffer': All sample times must be discrete. No continuous or constant sample times are allowed. I dont understand this error message in the configuration parametersthe solver options type are: fixed step and the solver is setting up to: discrete no continuos states. Look at the image and at the simulink model <file:prova1hardware.zip> attached here.