Error in Truetime integration with MPC controller in 'highway lane following model'

I have found this error when I implemeting highway lane following model with truetime . the error states as "Variable-step model 'HighwayLaneFollowingTestBench' references (via Model block 'HighwayLaneFollowingTestBench/Lane Following Controller') fixed-step model 'LaneFollowingController', which contains blocks with continuous and discrete sample times. Referencing a fixed-step model that contains both discrete and continuous components from a variable-step model is not supported."

Any pathway how to solve this?