Vgs exceeding in the PSS analysis

I am doing PSS analysis to calculate the THD. I ran the simulation for all blocks separately and everything is fine, but when I place then as a chain, I receive a Vgs exceeding warning. I checked everything and nothing look odd but the Vgs goes to higher than 20 V while the supply voltage is less than 5 V. Surprisingly, I do not get this warning when I do the Transient simulation with the exact same setup. Has anyone faced this problem before?

My cadence version: IC6.1.6-64b.500.6

Thanks!