ode15s works, but not with my Jacobian

Hi!

Thanks for looking at the problem!

Part of the code:

options=odeset('Jacobian',@J);
[tn,C]=ode15s(@F,[tinitial tfinal], C0, options);

The functions are defined with variables: J(tn,C) and F(tn,C)

1. When I don't use options, my system is solved fine.

2. When I do use the option to include the Jacobian, the following error occurs:

Error using  * 
Inner matrix dimensions must agree.

Error in ode15s (line 387)
    DfDt = dfdt + dfdy*yp;

Error in myprogram (line 23)
[tn,C]=ode15s(@F,[tinitial tfinal], C0, options);

I used keyboard to see if the function Jacobian is being called. This is not the case. Where could the error come from then?

Thanks a lot in advance!