audit net 问题

用cadence作simulation,audit net 只有出现下面的问题：

ERROR >> At least two Nets should have VOLTAGE property. Only one is found.
ERROR >> 1 Net(s) without drivers or receivers.

模型也指定了，DC也设置了，不知道是什么问题，1 Net(s) without drivers or receivers难道是模型引起的?

请大虾们指点，谢谢！