Problem with fsolve in a minimization algorithm

I have a problem with fsolve function. In particular, I have written a code which minimizes a function (called OBJECTIVE FUNCTION, line 433) so that the difference between the experimental values (yCH4out, lines 98 - 106) and the ones obtained by the solution of an ODE system (lines 328 - 368) is minimized. This ODE system depends on a variable, called K_CO, which is computed from the solution of an fsolve function, find_K_CO, (lines 437 - 443). The value of K_CO is to be obtained for every step of the integration in the ODE system, as it depends on P_CO, which changes as the integration moves on. So, the fsolve function should zero the equation for each integration step. I am quite sure that the error is inside the fsolve function (ines 437 - 443), as the remaining part of the code works if a constant value of K_CO is assumed. I think that the error comes from the way I have expressed all the variables the equation I want to nullify depends on: the ones listed in the global (line 439) or T (line 437).

Thank you very much in advance.

RIccardo Rinaldi.