MATLAB modelling "Block error"

hello....i have a question about matlab...when i running my simulation..matlab give instruction

"Derivative input 1 of 'test2/Subsystem/Integrator' at time 0.0 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)"

before this. my problem about error of complexity. but when i put abs and "sqrt(complex(x)) in my formula. this problem come out hope you can help me solve this problem..thank you