Simulink: warning Log in zero in one function

[Ana_]

Hello,
I have this problem (warning: log of zero in one function) when i try to simulate one system which apparentely doesn't have any problem.
in order to follow with my project i need to know how to change something parameters or whatever that is doing that my equation give me this mistake.
The equation is:

where all the dates i put are temperatures calculated with another equations with integrator blocks.
how can i do to can change the initial values and the equation could work?

 

[mfb]

Did you check if ##\Delta T_A## is zero somewhere? If yes, what should Simulink do in this case? If no, there should be no log of zero involved.