Solver problem in Simscape

Greetings,

I have to do a simscape simulation of a DC motor-generator coupling. Motor electrical circuit has a resistor and inductor. Generator is free loaded at first, which means there is only rotational inertia involved.

Input voltage is a step of 4 Volts. I used a S-PS converter and put it on a controlled voltage source into the motor electrical circuit. A solver block is present.

When I try to run the simulation, the following error is displayed:

"Nonlinear solver: Linear Algebra error. Failed to solve using iteration matrix. Initial conditions solve failed to converge."

Can I have help on this one? I fail to understand the error... I'm using Matlab 2009b, but the school also has more recent versions.

Regards,

Jules