"Derivative input 1 at time is Inf or NaN. Stopping simulation. There may be a singularity in the solution. If not, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)

hello, these error keep happening to me. i have tried put the unit delay, changes the solver, change the initial state, reducing step size but it fail every time i do. can someone help me? i need the answer as soon as possible. btw i'm using matlab 2012b. i attached the screenshot model.