Error while connecting a dc source to a full bridge inverter

I have generated the simulink model of the full bridge sine PWM and gate pulse waveform perfectly simulated. When I tried to connect it to a full bridge inverter module using ideal switches, an error reported:

*'...\DC voltage source:Initialization commands cannot be evaluated.'***

Any idea what is wrong with this dc source? I have selected the dc source from simulink/simpower Electronics/Electrical/ Sources/ dc voltage source.

Regards,

Roy