Dear Syed,
Perhaps there is some sort of incompatibility between the old FAST_SFunc.mexw64 file provided for FAST v7 and MATLAB/Simulink 2018? I’m not an expert on the Simulink interface. Perhaps someone else on this forum can comment on that.
From the forum topic you referenced, it sounds like you want to use FAST v7 due to its linearization capability. But it was not possible in FAST v7 to perform a linearization analysis when using the Simulink-FAST v7 interface anyway. Perhaps you could change your process so that you use the FAST v7 executable (without the MATLAB/Simulink interface) to generate the linear state-space models and use the Simulink-FAST v8 interface to run nonlinear time-domain simulations?
Best regards,