Help with VCO simulation using SpectreRF

Currently i'm doing a project about RF VCO design, working frequency is 5.5G. I have designed the circuit, and transiant analysis can be done correctly.
But when i do pss, the error message "Zero Diagonal found in Jacobian at N* gate1"; i really don't understand what's the error about.
Anyone who knows this, can kindly help me?
thanks very much!

It means that you have some convergence problems. Check them out below..
- Your VCO starts by itself without any extra components ?
- Some convergence problems could be solved by connecting 1 G Ohm resistances to the ground.
-PSS doesn't like short circuited transistors or components for matching purposes..
-Use initial state for problematic nodes by using "simulation convergence aids"..
-Decrease accuracy levels..or resetup the simulation parameters.
-Use Gear2
Something like those...

GL