I also encountered this problem, when I run a low bandgap circuit
I also encountered this problem, when I run a low voltage bandgap circuit or have many iteration circuit such PLL or ADC.
The reason is that Hspice can't the exact solution or can't convergence.
Solution
1. Use newest Hspice 2009.03.
2. This circuit has may stable solution. But Hspice can't find what you want. Add a start-up circuit to make sure that Hspice can convergence.