help on error : failed to evalute jacobian

hi everyone,
i am using comsol 4.2, and i want to plot\solve the temperature field the is generated around a gryogenic probe.
i have a datasheet of the change of temperature of the probe in time (inside the liquid nirtogen passes in a closed loop,but that is irrelevant because i have the temperature data)
i tried solving the time dependent problem and got the next error :

Failed to evaluate variable Jacobian.
- Variable: T1
- Geometry: 1
- Boundary: 9 10 11 15

plz help me

tahnks in advance

yuval
ps.
i would gladly send my model if it would hrlp