DAE is structurally inconsistent - Induced current in coil

Hello,

I am just starting to use COMSOL (4.3b) and I have encountered a problem while modelling. I am modelling two identical multi- turn coils where from one is excited by sinusoidal voltage source and I need to find the current generated in the second coil. For this I am using a 2D axisymmetric dimension, the Magnetic Fields (mf) and Electrical Circuit (cir) physics and a time dependent study. The circuit is a basic transformer circuit where the two inductors have been replaced by the coils (via the External I vs U component). When I compute, it displays this:

Errors during the multiphysics.

The DAE is structurally inconsistent.
-Variables:2
-Equation:1

Yet when I put an inductor in parallel with the coils, everything works and I don't see why.

Can someone help ?

Thanks