MATLAB expression 'slip_i' is not numeric. Block kinemat (#55) While executing: State During Action

hi, in the expression which i showed here is giving me the error which i mentioned in the question. values other than slip_o1 are simple constants. when i run this a single script file alone its working. but if i call it from the simulink block it is showing the error.

syms slip_i1 real slip_i = -(vpa(solve(T_i-(sigma*(1-(K/(slip_i1*l)*(1-exp(-slip_i1*l/K))))))));

syms slip_o1 real slip_o = -(vpa(solve(T_o-(sigma*(1-(K/(slip_o1*l)*(1-exp(-slip_o1*l/K))))))));

please help me with it.

Advance Thank you