Measure the tissue death

Hello,

I am trying to used a first order Arrhenius model to measure the tissue death in tumor ablation using Radiofrequency ablation technique in COMSOL.

I have done the following steps:
1. change the Arrhenius model (integral equation, see the attachement enclosed with this message) to differential equation;
2. define the differential equation in the COMSOL->Physics->Global Equations;
3. and then, simulate the Radiofrequency ablation model.
But there is a error, saying:
"Error: 6250
Failed to evaluate variable Jacobian.
-Variable: T
-Global scope"

Hope someone can help me figure this error out for me.
By the way, I am a new learner of COMSOL.

Thanks a lot.